diff --git a/src/app/Http/Controllers/API/SignupController.php b/src/app/Http/Controllers/API/SignupController.php
--- a/src/app/Http/Controllers/API/SignupController.php
+++ b/src/app/Http/Controllers/API/SignupController.php
@@ -12,6 +12,7 @@
 use App\Rules\UserEmailDomain;
 use App\Rules\UserEmailLocal;
 use App\SignupCode;
+use App\SignupInvitation;
 use App\User;
 use Illuminate\Http\Request;
 use Illuminate\Support\Facades\DB;
@@ -113,6 +114,33 @@
         return response()->json(['status' => 'success', 'code' => $code->code]);
     }
 
+    /**
+     * Returns signup invitation information.
+     *
+     * @param string $id Signup invitation identifier
+     *
+     * @return \Illuminate\Http\JsonResponse|void
+     */
+    public function invitation($id)
+    {
+        $invitation = SignupInvitation::withEnvTenant()->find($id);
+
+        if (empty($invitation) || $invitation->isCompleted()) {
+            return $this->errorResponse(404);
+        }
+
+        $has_domain = $this->getPlan()->hasDomain();
+
+        $result = [
+            'id' => $id,
+            'is_domain' => $has_domain,
+            'domains' => $has_domain ? [] : Domain::getPublicDomains(),
+        ];
+
+        return response()->json($result);
+    }
+
+
     /**
      * Validation of the verification code.
      *
@@ -190,10 +218,50 @@
             return response()->json(['status' => 'error', 'errors' => $v->errors()], 422);
         }
 
-        // Validate verification codes (again)
-        $v = $this->verify($request);
-        if ($v->status() !== 200) {
-            return $v;
+        // Signup via invitation
+        if ($request->invitation) {
+            $invitation = SignupInvitation::withEnvTenant()->find($request->invitation);
+
+            if (empty($invitation) || $invitation->isCompleted()) {
+                return $this->errorResponse(404);
+            }
+
+            // Check required fields
+            $v = Validator::make(
+                $request->all(),
+                [
+                    'first_name' => 'max:128',
+                    'last_name' => 'max:128',
+                    'voucher' => 'max:32',
+                ]
+            );
+
+            $errors = $v->fails() ? $v->errors()->toArray() : [];
+
+            if (!empty($errors)) {
+                return response()->json(['status' => 'error', 'errors' => $errors], 422);
+            }
+
+            $settings = [
+                'external_email' => $invitation->email,
+                'first_name' => $request->first_name,
+                'last_name' => $request->last_name,
+            ];
+        } else {
+            // Validate verification codes (again)
+            $v = $this->verify($request);
+            if ($v->status() !== 200) {
+                return $v;
+            }
+
+            // Get user name/email from the verification code database
+            $code_data = $v->getData();
+
+            $settings = [
+                'external_email' => $code_data->email,
+                'first_name' => $code_data->first_name,
+                'last_name' => $code_data->last_name,
+            ];
         }
 
         // Find the voucher discount
@@ -219,10 +287,6 @@
             return response()->json(['status' => 'error', 'errors' => $errors], 422);
         }
 
-        // Get user name/email from the verification code database
-        $code_data  = $v->getData();
-        $user_email = $code_data->email;
-
         // We allow only ASCII, so we can safely lower-case the email address
         $login = Str::lower($login);
         $domain_name = Str::lower($domain_name);
@@ -254,14 +318,19 @@
         $user->assignPlan($plan, $domain);
 
         // Save the external email and plan in user settings
-        $user->setSettings([
-                'external_email' => $user_email,
-                'first_name' => $code_data->first_name,
-                'last_name' => $code_data->last_name,
-        ]);
+        $user->setSettings($settings);
+
+        // Update the invitation
+        if (!empty($invitation)) {
+            $invitation->status = SignupInvitation::STATUS_COMPLETED;
+            $invitation->user_id = $user->id;
+            $invitation->save();
+        }
 
         // Remove the verification code
-        $this->code->delete();
+        if ($this->code) {
+            $this->code->delete();
+        }
 
         DB::commit();
 
diff --git a/src/app/Http/Controllers/API/V4/Reseller/InvitationsController.php b/src/app/Http/Controllers/API/V4/Reseller/InvitationsController.php
new file mode 100644
--- /dev/null
+++ b/src/app/Http/Controllers/API/V4/Reseller/InvitationsController.php
@@ -0,0 +1,251 @@
+<?php
+
+namespace App\Http\Controllers\API\V4\Reseller;
+
+use App\Http\Controllers\Controller;
+use App\SignupInvitation;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Validator;
+
+class InvitationsController extends Controller
+{
+    /**
+     * Show the form for creating a new resource.
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function create()
+    {
+        return $this->errorResponse(404);
+    }
+
+    /**
+     * Remove the specified invitation.
+     *
+     * @param int $id Invitation identifier
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function destroy($id)
+    {
+        $invitation = SignupInvitation::withUserTenant()->find($id);
+
+        if (empty($invitation)) {
+            return $this->errorResponse(404);
+        }
+
+        $invitation->delete();
+
+        return response()->json([
+                'status' => 'success',
+                'message' => trans('app.signup-invitation-delete-success'),
+        ]);
+    }
+
+    /**
+     * Show the form for editing the specified resource.
+     *
+     * @param int $id Invitation identifier
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function edit($id)
+    {
+        return $this->errorResponse(404);
+    }
+
+    /**
+     * Display a listing of the resource.
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function index()
+    {
+        $pageSize = 10;
+        $search = request()->input('search');
+        $page = intval(request()->input('page')) ?: 1;
+        $hasMore = false;
+
+        $result = SignupInvitation::withUserTenant()
+            ->latest()
+            ->limit($pageSize + 1)
+            ->offset($pageSize * ($page - 1));
+
+        if ($search) {
+            if (strpos($search, '@')) {
+                $result->where('email', $search);
+            } else {
+                $result->whereLike('email', $search);
+            }
+        }
+
+        $result = $result->get();
+
+        if (count($result) > $pageSize) {
+            $result->pop();
+            $hasMore = true;
+        }
+
+        $result = $result->map(function ($invitation) {
+            return $this->invitationToArray($invitation);
+        });
+
+        return response()->json([
+                'status' => 'success',
+                'list' => $result,
+                'count' => count($result),
+                'hasMore' => $hasMore,
+                'page' => $page,
+        ]);
+    }
+
+    /**
+     * Resend the specified invitation.
+     *
+     * @param int $id Invitation identifier
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function resend($id)
+    {
+        $invitation = SignupInvitation::withUserTenant()->find($id);
+
+        if (empty($invitation)) {
+            return $this->errorResponse(404);
+        }
+
+        if ($invitation->isFailed() || $invitation->isSent()) {
+            // Note: The email sending job will be dispatched by the observer
+            $invitation->status = SignupInvitation::STATUS_NEW;
+            $invitation->save();
+        }
+
+        return response()->json([
+                'status' => 'success',
+                'message' => trans('app.signup-invitation-resend-success'),
+                'invitation' => $this->invitationToArray($invitation),
+        ]);
+    }
+
+    /**
+     * Store a newly created resource in storage.
+     *
+     * @param \Illuminate\Http\Request $request
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function store(Request $request)
+    {
+        $errors = [];
+        $invitations = [];
+
+        if (!empty($request->file) && is_object($request->file)) {
+            // Expected a text/csv file with multiple email addresses
+            if (!$request->file->isValid()) {
+                $errors = ['file' => [$request->file->getErrorMessage()]];
+            } else {
+                $fh = fopen($request->file->getPathname(), 'r');
+                $line_number = 0;
+                $error = null;
+
+                while ($line = fgetcsv($fh)) {
+                    $line_number++;
+
+                    if (count($line) >= 1 && $line[0]) {
+                        $email = trim($line[0]);
+
+                        if (strpos($email, '@')) {
+                            $v = Validator::make(['email' => $email], ['email' => 'email:filter|required']);
+
+                            if ($v->fails()) {
+                                $args = ['email' => $email, 'line' => $line_number];
+                                $error = trans('app.signup-invitations-csv-invalid-email', $args);
+                                break;
+                            }
+
+                            $invitations[] = ['email' => $email];
+                        }
+                    }
+                }
+
+                fclose($fh);
+
+                if ($error) {
+                    $errors = ['file' => $error];
+                } elseif (empty($invitations)) {
+                    $errors = ['file' => trans('app.signup-invitations-csv-empty')];
+                }
+            }
+        } else {
+            // Expected 'email' field with an email address
+            $v = Validator::make($request->all(), ['email' => 'email|required']);
+
+            if ($v->fails()) {
+                $errors = $v->errors()->toArray();
+            } else {
+                $invitations[] = ['email' => $request->email];
+            }
+        }
+
+        if (!empty($errors)) {
+            return response()->json(['status' => 'error', 'errors' => $errors], 422);
+        }
+
+        $count = 0;
+        foreach ($invitations as $idx => $invitation) {
+            SignupInvitation::create($invitation);
+            $count++;
+        }
+
+        return response()->json([
+                'status' => 'success',
+                'message' => \trans_choice('app.signup-invitations-created', $count, ['count' => $count]),
+                'count' => $count,
+        ]);
+    }
+
+    /**
+     * Display the specified resource.
+     *
+     * @param int $id Invitation identifier
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function show($id)
+    {
+        return $this->errorResponse(404);
+    }
+
+    /**
+     * Update the specified resource in storage.
+     *
+     * @param \Illuminate\Http\Request $request
+     * @param int                      $id
+     *
+     * @return \Illuminate\Http\JsonResponse
+     */
+    public function update(Request $request, $id)
+    {
+        return $this->errorResponse(404);
+    }
+
+    /**
+     * Convert an invitation object to an array for output
+     *
+     * @param \App\SignupInvitation $invitation The signup invitation object
+     *
+     * @return array
+     */
+    protected static function invitationToArray(SignupInvitation $invitation): array
+    {
+        return [
+            'id' => $invitation->id,
+            'email' => $invitation->email,
+            'isNew' => $invitation->isNew(),
+            'isSent' => $invitation->isSent(),
+            'isFailed' => $invitation->isFailed(),
+            'isCompleted' => $invitation->isCompleted(),
+            'created' => $invitation->created_at->toDateTimeString(),
+        ];
+    }
+}
diff --git a/src/app/Jobs/SignupInvitationEmail.php b/src/app/Jobs/SignupInvitationEmail.php
new file mode 100644
--- /dev/null
+++ b/src/app/Jobs/SignupInvitationEmail.php
@@ -0,0 +1,75 @@
+<?php
+
+namespace App\Jobs;
+
+use App\SignupInvitation;
+use App\Mail\SignupInvitation as SignupInvitationMail;
+use Illuminate\Bus\Queueable;
+use Illuminate\Contracts\Queue\ShouldQueue;
+use Illuminate\Foundation\Bus\Dispatchable;
+use Illuminate\Support\Facades\Mail;
+use Illuminate\Queue\SerializesModels;
+use Illuminate\Queue\InteractsWithQueue;
+
+class SignupInvitationEmail implements ShouldQueue
+{
+    use Dispatchable;
+    use InteractsWithQueue;
+    use Queueable;
+    use SerializesModels;
+
+    /** @var int The number of times the job may be attempted. */
+    public $tries = 3;
+
+    /** @var bool Delete the job if its models no longer exist. */
+    public $deleteWhenMissingModels = true;
+
+    /** @var int The number of seconds to wait before retrying the job. */
+    public $retryAfter = 10;
+
+    /** @var SignupInvitation Signup invitation object */
+    protected $invitation;
+
+
+    /**
+     * Create a new job instance.
+     *
+     * @param SignupInvitation $invitation Invitation object
+     *
+     * @return void
+     */
+    public function __construct(SignupInvitation $invitation)
+    {
+        $this->invitation = $invitation;
+    }
+
+    /**
+     * Execute the job.
+     *
+     * @return void
+     */
+    public function handle()
+    {
+        Mail::to($this->invitation->email)->send(new SignupInvitationMail($this->invitation));
+
+        // Update invitation status
+        $this->invitation->status = SignupInvitation::STATUS_SENT;
+        $this->invitation->save();
+    }
+
+    /**
+     * The job failed to process.
+     *
+     * @param \Exception $exception
+     *
+     * @return void
+     */
+    public function failed(\Exception $exception)
+    {
+        if ($this->attempts() >= $this->tries) {
+            // Update invitation status
+            $this->invitation->status = SignupInvitation::STATUS_FAILED;
+            $this->invitation->save();
+        }
+    }
+}
diff --git a/src/app/Mail/SignupInvitation.php b/src/app/Mail/SignupInvitation.php
new file mode 100644
--- /dev/null
+++ b/src/app/Mail/SignupInvitation.php
@@ -0,0 +1,72 @@
+<?php
+
+namespace App\Mail;
+
+use App\SignupInvitation as SI;
+use App\Utils;
+use Illuminate\Bus\Queueable;
+use Illuminate\Mail\Mailable;
+use Illuminate\Queue\SerializesModels;
+use Illuminate\Support\Str;
+
+class SignupInvitation extends Mailable
+{
+    use Queueable;
+    use SerializesModels;
+
+    /** @var \App\SignupInvitation A signup invitation object */
+    protected $invitation;
+
+
+    /**
+     * Create a new message instance.
+     *
+     * @param \App\SignupInvitation $invitation A signup invitation object
+     *
+     * @return void
+     */
+    public function __construct(SI $invitation)
+    {
+        $this->invitation = $invitation;
+    }
+
+    /**
+     * Build the message.
+     *
+     * @return $this
+     */
+    public function build()
+    {
+        $href = Utils::serviceUrl('/signup/invite/' . $this->invitation->id);
+
+        $this->view('emails.html.signup_invitation')
+            ->text('emails.plain.signup_invitation')
+            ->subject(__('mail.signupinvitation-subject', ['site' => \config('app.name')]))
+            ->with([
+                    'site' => \config('app.name'),
+                    'href' => $href,
+            ]);
+
+        return $this;
+    }
+
+    /**
+     * Render the mail template with fake data
+     *
+     * @param string $type Output format ('html' or 'text')
+     *
+     * @return string HTML or Plain Text output
+     */
+    public static function fakeRender(string $type = 'html'): string
+    {
+        $invitation = new SI([
+                'email' => 'test@external.org',
+        ]);
+
+        $invitation->id = Utils::uuidStr();
+
+        $mail = new self($invitation);
+
+        return Helper::render($mail, $type);
+    }
+}
diff --git a/src/app/Observers/SignupInvitationObserver.php b/src/app/Observers/SignupInvitationObserver.php
new file mode 100644
--- /dev/null
+++ b/src/app/Observers/SignupInvitationObserver.php
@@ -0,0 +1,65 @@
+<?php
+
+namespace App\Observers;
+
+use App\SignupInvitation as SI;
+
+/**
+ * This is an observer for the SignupInvitation model definition.
+ */
+class SignupInvitationObserver
+{
+    /**
+     * Ensure the invitation ID is a custom ID (uuid).
+     *
+     * @param \App\SignupInvitation $invitation The invitation object
+     *
+     * @return void
+     */
+    public function creating(SI $invitation)
+    {
+        while (true) {
+            $allegedly_unique = \App\Utils::uuidStr();
+            if (!SI::find($allegedly_unique)) {
+                $invitation->{$invitation->getKeyName()} = $allegedly_unique;
+                break;
+            }
+        }
+
+        $invitation->status = SI::STATUS_NEW;
+
+        $invitation->tenant_id = \config('app.tenant_id');
+    }
+
+    /**
+     * Handle the invitation "created" event.
+     *
+     * @param \App\SignupInvitation $invitation The invitation object
+     *
+     * @return void
+     */
+    public function created(SI $invitation)
+    {
+        \App\Jobs\SignupInvitationEmail::dispatch($invitation);
+    }
+
+    /**
+     * Handle the invitation "updated" event.
+     *
+     * @param \App\SignupInvitation $invitation The invitation object
+     *
+     * @return void
+     */
+    public function updated(SI $invitation)
+    {
+        $oldStatus = $invitation->getOriginal('status');
+
+        // Resend the invitation
+        if (
+            $invitation->status == SI::STATUS_NEW
+            && ($oldStatus == SI::STATUS_FAILED || $oldStatus == SI::STATUS_SENT)
+        ) {
+            \App\Jobs\SignupInvitationEmail::dispatch($invitation);
+        }
+    }
+}
diff --git a/src/app/Providers/AppServiceProvider.php b/src/app/Providers/AppServiceProvider.php
--- a/src/app/Providers/AppServiceProvider.php
+++ b/src/app/Providers/AppServiceProvider.php
@@ -36,6 +36,7 @@
         \App\PackageSku::observe(\App\Observers\PackageSkuObserver::class);
         \App\Plan::observe(\App\Observers\PlanObserver::class);
         \App\SignupCode::observe(\App\Observers\SignupCodeObserver::class);
+        \App\SignupInvitation::observe(\App\Observers\SignupInvitationObserver::class);
         \App\Sku::observe(\App\Observers\SkuObserver::class);
         \App\Transaction::observe(\App\Observers\TransactionObserver::class);
         \App\User::observe(\App\Observers\UserObserver::class);
@@ -84,5 +85,24 @@
             /** @var Builder $this */
             return $this->whereNull(($table ? "$table." : '') . 'tenant_id');
         });
+
+        // Query builder 'whereLike' mocro
+        Builder::macro('whereLike', function (string $column, string $search, int $mode = 0) {
+            $search = addcslashes($search, '%_');
+
+            switch ($mode) {
+                case 2:
+                    $search .= '%';
+                    break;
+                case 1:
+                    $search = '%' . $search;
+                    break;
+                default:
+                    $search = '%' . $search . '%';
+            }
+
+            /** @var Builder $this */
+            return $this->where($column, 'like', $search);
+        });
     }
 }
diff --git a/src/app/SignupInvitation.php b/src/app/SignupInvitation.php
new file mode 100644
--- /dev/null
+++ b/src/app/SignupInvitation.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace App;
+
+use Carbon\Carbon;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * The eloquent definition of a signup invitation.
+ *
+ * @property string       $email
+ * @property string       $id
+ * @property ?int         $tenant_id
+ * @property ?\App\Tenant $tenant
+ * @property ?\App\User   $user
+ */
+class SignupInvitation extends Model
+{
+    // just created
+    public const STATUS_NEW     = 1 << 0;
+    // it's been sent successfully
+    public const STATUS_SENT    = 1 << 1;
+    // sending failed
+    public const STATUS_FAILED  = 1 << 2;
+    // the user signed up
+    public const STATUS_COMPLETED = 1 << 3;
+
+
+    /**
+     * Indicates if the IDs are auto-incrementing.
+     *
+     * @var bool
+     */
+    public $incrementing = false;
+
+    /**
+     * The "type" of the auto-incrementing ID.
+     *
+     * @var string
+     */
+    protected $keyType = 'string';
+
+    /**
+     * The attributes that are mass assignable.
+     *
+     * @var array
+     */
+    protected $fillable = ['email'];
+
+    /**
+     * Returns whether this invitation process completed (user signed up)
+     *
+     * @return bool
+     */
+    public function isCompleted(): bool
+    {
+        return ($this->status & self::STATUS_COMPLETED) > 0;
+    }
+
+    /**
+     * Returns whether this invitation sending failed.
+     *
+     * @return bool
+     */
+    public function isFailed(): bool
+    {
+        return ($this->status & self::STATUS_FAILED) > 0;
+    }
+
+    /**
+     * Returns whether this invitation is new.
+     *
+     * @return bool
+     */
+    public function isNew(): bool
+    {
+        return ($this->status & self::STATUS_NEW) > 0;
+    }
+
+    /**
+     * Returns whether this invitation has been sent.
+     *
+     * @return bool
+     */
+    public function isSent(): bool
+    {
+        return ($this->status & self::STATUS_SENT) > 0;
+    }
+
+    /**
+     * The tenant for this invitation.
+     *
+     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function tenant()
+    {
+        return $this->belongsTo('App\Tenant', 'tenant_id', 'id');
+    }
+
+    /**
+     * The account to which the invitation was used for.
+     *
+     * @return \Illuminate\Database\Eloquent\Relations\BelongsTo
+     */
+    public function user()
+    {
+        return $this->belongsTo('App\User', 'user_id', 'id');
+    }
+}
diff --git a/src/app/Tenant.php b/src/app/Tenant.php
--- a/src/app/Tenant.php
+++ b/src/app/Tenant.php
@@ -27,4 +27,14 @@
     {
         return $this->hasMany('App\Discount');
     }
+
+    /**
+     * SignupInvitations assigned to this tenant.
+     *
+     * @return \Illuminate\Database\Eloquent\Relations\HasMany
+     */
+    public function signupInvitations()
+    {
+        return $this->hasMany('App\SignupInvitation');
+    }
 }
diff --git a/src/database/migrations/2021_03_26_080000_create_signup_invitations_table.php b/src/database/migrations/2021_03_26_080000_create_signup_invitations_table.php
new file mode 100644
--- /dev/null
+++ b/src/database/migrations/2021_03_26_080000_create_signup_invitations_table.php
@@ -0,0 +1,49 @@
+<?php
+
+use Illuminate\Support\Facades\Schema;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Database\Migrations\Migration;
+
+// phpcs:ignore
+class CreateSignupInvitationsTable extends Migration
+{
+    /**
+     * Run the migrations.
+     *
+     * @return void
+     */
+    public function up()
+    {
+        Schema::create(
+            'signup_invitations',
+            function (Blueprint $table) {
+                $table->string('id', 36);
+                $table->string('email');
+                $table->smallInteger('status');
+                $table->bigInteger('user_id')->nullable();
+                $table->bigInteger('tenant_id')->unsigned()->nullable();
+                $table->timestamps();
+
+                $table->primary('id');
+
+                $table->index('email');
+                $table->index('created_at');
+
+                $table->foreign('tenant_id')->references('id')->on('tenants')
+                    ->onUpdate('cascade')->onDelete('set null');
+                $table->foreign('user_id')->references('id')->on('users')
+                    ->onUpdate('cascade')->onDelete('set null');
+            }
+        );
+    }
+
+    /**
+     * Reverse the migrations.
+     *
+     * @return void
+     */
+    public function down()
+    {
+        Schema::dropIfExists('signup_invitations');
+    }
+}
diff --git a/src/phpstan.neon b/src/phpstan.neon
--- a/src/phpstan.neon
+++ b/src/phpstan.neon
@@ -7,10 +7,12 @@
         - '#Access to an undefined property Illuminate\\Database\\Eloquent\\Model::\$id#'
         - '#Access to an undefined property Illuminate\\Database\\Eloquent\\Model::\$created_at#'
         - '#Call to an undefined method Illuminate\\Database\\Eloquent\\Model::toString\(\)#'
-        - '#Call to an undefined method Illuminate\\Database\\Eloquent\\Builder[^:]*::withEnvTenant\(\)#'
-        - '#Call to an undefined method Illuminate\\Database\\Eloquent\\Builder[^:]*::withUserTenant\(\)#'
+        - '#Call to an undefined [a-zA-Z0-9<>\\ ]+::withEnvTenant\(\)#'
+        - '#Call to an undefined [a-zA-Z0-9<>\\ ]+::withUserTenant\(\)#'
         - '#Call to an undefined method Tests\\Browser::#'
     level: 4
+    parallel:
+        processTimeout: 300.0
     paths:
         - app/
         - tests/
diff --git a/src/resources/js/app.js b/src/resources/js/app.js
--- a/src/resources/js/app.js
+++ b/src/resources/js/app.js
@@ -425,7 +425,7 @@
                     }
 
                     if (input.length) {
-                        // Create an error message\
+                        // Create an error message
                         // API responses can use a string, array or object
                         let msg_text = ''
                         if ($.type(msg) !== 'string') {
diff --git a/src/resources/js/reseller/routes.js b/src/resources/js/reseller/routes.js
--- a/src/resources/js/reseller/routes.js
+++ b/src/resources/js/reseller/routes.js
@@ -1,5 +1,6 @@
 import DashboardComponent from '../../vue/Reseller/Dashboard'
 import DomainComponent from '../../vue/Admin/Domain'
+import InvitationsComponent from '../../vue/Reseller/Invitations'
 import LoginComponent from '../../vue/Login'
 import LogoutComponent from '../../vue/Logout'
 import PageComponent from '../../vue/Page'
@@ -33,6 +34,12 @@
         name: 'logout',
         component: LogoutComponent
     },
+    {
+        path: '/invitations',
+        name: 'invitations',
+        component: InvitationsComponent,
+        meta: { requiresAuth: true }
+    },
 /*
     {
         path: '/stats',
diff --git a/src/resources/js/user/routes.js b/src/resources/js/user/routes.js
--- a/src/resources/js/user/routes.js
+++ b/src/resources/js/user/routes.js
@@ -76,6 +76,11 @@
         component: MeetComponent,
         meta: { requiresAuth: true }
     },
+    {
+        path: '/signup/invite/:param',
+        name: 'signup-invite',
+        component: SignupComponent
+    },
     {
         path: '/signup/:param?',
         alias: '/signup/voucher/:param',
diff --git a/src/resources/lang/en/app.php b/src/resources/lang/en/app.php
--- a/src/resources/lang/en/app.php
+++ b/src/resources/lang/en/app.php
@@ -45,6 +45,12 @@
     'search-foundxdomains' => ':x domains have been found.',
     'search-foundxusers' => ':x user accounts have been found.',
 
+    'signup-invitations-created' => 'The invitation has been created.|:count invitations has been created.',
+    'signup-invitations-csv-empty' => 'Failed to find any valid email addresses in the uploaded file.',
+    'signup-invitations-csv-invalid-email' => 'Found an invalid email address (:email) on line :line.',
+    'signup-invitation-delete-success' => 'Invitation deleted successfully.',
+    'signup-invitation-resend-success' => 'Invitation added to the sending queue successfully.',
+
     'support-request-success' => 'Support request submitted successfully.',
     'support-request-error' => 'Failed to submit the support request.',
 
diff --git a/src/resources/lang/en/mail.php b/src/resources/lang/en/mail.php
--- a/src/resources/lang/en/mail.php
+++ b/src/resources/lang/en/mail.php
@@ -75,6 +75,11 @@
     'signupcode-body1' => "This is your verification code for the :site registration process:",
     'signupcode-body2' => "You can also click the link below to continue the registration process:",
 
+    'signupinvitation-subject' => ":site Invitation",
+    'signupinvitation-header' => "Hi,",
+    'signupinvitation-body1' => "You have been invited to join :site. Click the link below to sign up.",
+    'signupinvitation-body2' => "",
+
     'suspendeddebtor-subject' => ":site Account Suspended",
     'suspendeddebtor-body' => "You have been behind on paying for your :site account "
         ."for over :days days. Your account has been suspended.",
diff --git a/src/resources/themes/app.scss b/src/resources/themes/app.scss
--- a/src/resources/themes/app.scss
+++ b/src/resources/themes/app.scss
@@ -115,7 +115,10 @@
 }
 
 table {
-    td.buttons,
+    th {
+        white-space: nowrap;
+    }
+
     td.email,
     td.price,
     td.datetime,
@@ -124,6 +127,7 @@
         white-space: nowrap;
     }
 
+    td.buttons,
     th.price,
     td.price {
         width: 1%;
@@ -279,6 +283,13 @@
             opacity: 0.6;
         }
 
+        // Some icons are too big, scale them down
+        &.link-invitations {
+            svg {
+                transform: scale(0.9);
+            }
+        }
+
         .badge {
             position: absolute;
             top: 0.5rem;
diff --git a/src/resources/views/emails/html/signup_invitation.blade.php b/src/resources/views/emails/html/signup_invitation.blade.php
new file mode 100644
--- /dev/null
+++ b/src/resources/views/emails/html/signup_invitation.blade.php
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<html lang="{{ str_replace('_', '-', app()->getLocale()) }}">
+    <head>
+        <meta charset="utf-8">
+    </head>
+    <body>
+        <p>{{ __('mail.signupinvitation-header') }}</p>
+
+        <p>{{ __('mail.signupinvitation-body1', ['site' => $site]) }}</p>
+
+        <p><a href="{!! $href !!}">{!! $href !!}</a></p>
+
+        <p>{{ __('mail.signupinvitation-body2') }}</p>
+
+        <p>{{ __('mail.footer1') }}</p>
+        <p>{{ __('mail.footer2', ['site' => $site]) }}</p>
+    </body>
+</html>
diff --git a/src/resources/views/emails/plain/signup_invitation.blade.php b/src/resources/views/emails/plain/signup_invitation.blade.php
new file mode 100644
--- /dev/null
+++ b/src/resources/views/emails/plain/signup_invitation.blade.php
@@ -0,0 +1,11 @@
+{!! __('mail.signupinvitation-header') !!}
+
+{!! __('mail.signupinvitation-body1', ['site' => $site]) !!}
+
+{!! $href !!}
+
+{!! __('mail.signupinvitation-body2') !!}
+
+-- 
+{!! __('mail.footer1') !!}
+{!! __('mail.footer2', ['site' => $site]) !!}
diff --git a/src/resources/vue/Reseller/Dashboard.vue b/src/resources/vue/Reseller/Dashboard.vue
--- a/src/resources/vue/Reseller/Dashboard.vue
+++ b/src/resources/vue/Reseller/Dashboard.vue
@@ -2,12 +2,19 @@
     <div class="container" dusk="dashboard-component">
         <user-search></user-search>
         <div id="dashboard-nav" class="mt-3">
+            <router-link class="card link-invitations" :to="{ name: 'invitations' }">
+                <svg-icon icon="envelope-open-text"></svg-icon><span class="name">Invitations</span>
+            </router-link>
         </div>
     </div>
 </template>
 
 <script>
     import UserSearch from '../Widgets/UserSearch'
+    import { library } from '@fortawesome/fontawesome-svg-core'
+    import { faEnvelopeOpenText } from '@fortawesome/free-solid-svg-icons'
+
+    library.add(faEnvelopeOpenText)
 
     export default {
         components: {
diff --git a/src/resources/vue/Reseller/Invitations.vue b/src/resources/vue/Reseller/Invitations.vue
new file mode 100644
--- /dev/null
+++ b/src/resources/vue/Reseller/Invitations.vue
@@ -0,0 +1,283 @@
+<template>
+    <div class="container">
+        <div class="card" id="invitations">
+            <div class="card-body">
+                <div class="card-title">
+                    Signup Invitations
+                </div>
+                <div class="card-text">
+                    <div class="mb-2 d-flex">
+                        <form @submit.prevent="searchInvitations" id="search-form" class="input-group" style="flex:1">
+                            <input class="form-control" type="text" placeholder="Email address or domain" v-model="search">
+                            <div class="input-group-append">
+                                <button type="submit" class="btn btn-primary"><svg-icon icon="search"></svg-icon> Search</button>
+                            </div>
+                        </form>
+                        <div>
+                            <button class="btn btn-success create-invite ml-1" @click="inviteUserDialog">
+                                <svg-icon icon="envelope-open-text"></svg-icon> Create invite(s)
+                            </button>
+                        </div>
+                    </div>
+
+                    <table id="invitations-list" class="table table-sm table-hover">
+                        <thead class="thead-light">
+                            <tr>
+                                <th scope="col">External Email</th>
+                                <th scope="col">Created</th>
+                                <th scope="col"></th>
+                            </tr>
+                        </thead>
+                        <tbody>
+                            <tr v-for="inv in invitations" :id="'i' + inv.id" :key="inv.id">
+                                <td class="email">
+                                    <svg-icon icon="envelope-open-text" :class="statusClass(inv)" :title="statusText(inv)"></svg-icon>
+                                    <span>{{ inv.email }}</span>
+                                </td>
+                                <td class="datetime">
+                                    {{ inv.created }}
+                                </td>
+                                <td class="buttons">
+                                    <button class="btn text-danger button-delete p-0 ml-1" @click="deleteInvite(inv.id)">
+                                        <svg-icon icon="trash-alt"></svg-icon>
+                                        <span class="btn-label">Delete</span>
+                                    </button>
+                                    <button class="btn button-resend p-0 ml-1" :disabled="inv.isNew || inv.isCompleted" @click="resendInvite(inv.id)">
+                                        <svg-icon icon="redo"></svg-icon>
+                                        <span class="btn-label">Resend</span>
+                                    </button>
+                                </td>
+                            </tr>
+                        </tbody>
+                        <tfoot class="table-fake-body">
+                            <tr>
+                                <td colspan="3">There are no invitations in the database.</td>
+                            </tr>
+                        </tfoot>
+                    </table>
+                    <div class="text-center p-3" id="more-loader" v-if="hasMore">
+                        <button class="btn btn-secondary" @click="loadInvitations(true)">Load more</button>
+                    </div>
+                </div>
+            </div>
+        </div>
+
+        <div id="invite-create" class="modal" tabindex="-1" role="dialog">
+            <div class="modal-dialog" role="document">
+                <div class="modal-content">
+                    <div class="modal-header">
+                        <h5 class="modal-title">Invite for a signup</h5>
+                        <button type="button" class="close" data-dismiss="modal" aria-label="Close">
+                            <span aria-hidden="true">&times;</span>
+                        </button>
+                    </div>
+                    <div class="modal-body">
+                        <form>
+                            <p>Enter an email address of the person you want to invite.</p>
+                            <div>
+                                <input id="email" type="text" class="form-control" name="email">
+                            </div>
+                            <div class="form-separator"><hr><span>or</span></div>
+                            <p>
+                                To send multiple invitations at once, provide a CSV (comma separated) file,
+                                or alternatively a plain-text file, containing one email address per line.
+                            </p>
+                            <div class="custom-file">
+                                <input id="file" type="file" class="custom-file-input" name="csv" @change="fileChange">
+                                <label class="custom-file-label" for="file">Choose file...</label>
+                            </div>
+                        </form>
+                    </div>
+                    <div class="modal-footer">
+                        <button type="button" class="btn btn-secondary modal-cancel" data-dismiss="modal">Cancel</button>
+                        <button type="button" class="btn btn-primary modal-action" @click="inviteUser()">
+                            <svg-icon icon="paper-plane"></svg-icon> Send invite(s)
+                        </button>
+                    </div>
+                </div>
+            </div>
+        </div>
+    </div>
+</template>
+
+<script>
+    import { library } from '@fortawesome/fontawesome-svg-core'
+    import { faEnvelopeOpenText, faPaperPlane, faRedo } from '@fortawesome/free-solid-svg-icons'
+
+    library.add(faEnvelopeOpenText, faPaperPlane, faRedo)
+
+    export default {
+        data() {
+            return {
+                invitations: [],
+                hasMore: false,
+                page: 1,
+                search: ''
+            }
+        },
+        mounted() {
+            this.$root.startLoading()
+            this.loadInvitations(null, () => this.$root.stopLoading())
+        },
+        methods: {
+            deleteInvite(id) {
+                axios.delete('/api/v4/invitations/' + id)
+                    .then(response => {
+                        if (response.data.status == 'success') {
+                            this.$toast.success(response.data.message)
+
+                            // Remove the invitation record from the list
+                            const index = this.invitations.findIndex(item => item.id == id)
+                            this.invitations.splice(index, 1)
+                        }
+                    })
+            },
+            fileChange(e) {
+                let label = 'Choose file...'
+                let files = e.target.files
+
+                if (files.length) {
+                    label = files[0].name
+                    if (files.length > 1) {
+                        label += ', ...'
+                    }
+                }
+
+                $(e.target).next().text(label)
+            },
+            inviteUser() {
+                let dialog = $('#invite-create')
+                let post = new FormData()
+                let params = { headers: { 'Content-Type': 'multipart/form-data' } }
+
+                post.append('email', dialog.find('#email').val())
+
+                this.$root.clearFormValidation(dialog.find('form'))
+
+                // Append the file to POST data
+                let files = dialog.find('#file').get(0).files
+                if (files.length) {
+                    post.append('file', files[0])
+                }
+
+                axios.post('/api/v4/invitations', post, params)
+                    .then(response => {
+                        if (response.data.status == 'success') {
+                            dialog.modal('hide')
+                            this.$toast.success(response.data.message)
+                            if (response.data.count) {
+                                this.loadInvitations({ reset: true })
+                            }
+                        }
+                    })
+            },
+            inviteUserDialog() {
+                let dialog = $('#invite-create')
+                let form = dialog.find('form')
+
+                form.get(0).reset()
+                this.fileChange({ target: form.find('#file')[0] }) // resets file input label
+                this.$root.clearFormValidation(form)
+
+                dialog.on('shown.bs.modal', () => {
+                    dialog.find('input').get(0).focus()
+                }).modal()
+            },
+            loadInvitations(params, callback) {
+                let loader
+                let get = {}
+
+                if (params) {
+                    if (params.reset) {
+                        this.invitations = []
+                        this.page = 0
+                    }
+
+                    get.page = params.page || (this.page + 1)
+
+                    if (typeof params === 'object' && 'search' in params) {
+                        get.search = params.search
+                        this.currentSearch = params.search
+                    } else {
+                        get.search = this.currentSearch
+                    }
+
+                    loader = $(get.page > 1 ? '#more-loader' : '#invitations-list tfoot td')
+                } else {
+                    this.currentSearch = null
+                }
+
+                this.$root.addLoader(loader)
+
+                axios.get('/api/v4/invitations', { params: get })
+                    .then(response => {
+                        this.$root.removeLoader(loader)
+
+                        // Note: In Vue we can't just use .concat()
+                        for (let i in response.data.list) {
+                            this.$set(this.invitations, this.invitations.length, response.data.list[i])
+                        }
+                        this.hasMore = response.data.hasMore
+                        this.page = response.data.page || 1
+
+                        if (callback) {
+                            callback()
+                        }
+                    })
+                    .catch(error => {
+                        this.$root.removeLoader(loader)
+
+                        if (callback) {
+                            callback()
+                        }
+                    })
+            },
+            resendInvite(id) {
+                axios.post('/api/v4/invitations/' + id + '/resend')
+                    .then(response => {
+                        if (response.data.status == 'success') {
+                            this.$toast.success(response.data.message)
+
+                            // Update the invitation record
+                            const index = this.invitations.findIndex(item => item.id == id)
+                            this.invitations.splice(index, 1)
+                            this.$set(this.invitations, index, response.data.invitation)
+                        }
+                    })
+            },
+            searchInvitations() {
+                this.loadInvitations({ reset: true, search: this.search })
+            },
+            statusClass(invitation) {
+                if (invitation.isCompleted) {
+                    return 'text-success'
+                }
+
+                if (invitation.isFailed) {
+                    return 'text-danger'
+                }
+
+                if (invitation.isSent) {
+                    return 'text-primary'
+                }
+
+                return ''
+            },
+            statusText(invitation) {
+                if (invitation.isCompleted) {
+                    return 'User signed up'
+                }
+
+                if (invitation.isFailed) {
+                    return 'Sending failed'
+                }
+
+                if (invitation.isSent) {
+                    return 'Sent'
+                }
+
+                return 'Not sent yet'
+            }
+        }
+    }
+</script>
diff --git a/src/resources/vue/Signup.vue b/src/resources/vue/Signup.vue
--- a/src/resources/vue/Signup.vue
+++ b/src/resources/vue/Signup.vue
@@ -1,6 +1,6 @@
 <template>
     <div class="container">
-        <div id="step0">
+        <div id="step0" v-if="!invitation">
             <div class="plan-selector card-deck">
                 <div v-for="item in plans" :key="item.id" :class="'card bg-light plan-' + item.title">
                     <div class="card-header plan-header">
@@ -16,7 +16,7 @@
             </div>
         </div>
 
-        <div class="card d-none" id="step1">
+        <div class="card d-none" id="step1" v-if="!invitation">
             <div class="card-body">
                 <h4 class="card-title">Sign Up - Step 1/3</h4>
                 <p class="card-text">
@@ -39,7 +39,7 @@
             </div>
         </div>
 
-        <div class="card d-none" id="step2">
+        <div class="card d-none" id="step2" v-if="!invitation">
             <div class="card-body">
                 <h4 class="card-title">Sign Up - Step 2/3</h4>
                 <p class="card-text">
@@ -60,20 +60,28 @@
 
         <div class="card d-none" id="step3">
             <div class="card-body">
-                <h4 class="card-title">Sign Up - Step 3/3</h4>
+                <h4 v-if="!invitation" class="card-title">Sign Up - Step 3/3</h4>
                 <p class="card-text">
                     Create your Kolab identity (you can choose additional addresses later).
                 </p>
                 <form @submit.prevent="submitStep3" data-validation-prefix="signup_">
+                    <div class="form-group" v-if="invitation">
+                        <div class="input-group">
+                            <input type="text" class="form-control" id="signup_first_name" placeholder="First Name" autofocus v-model="first_name">
+                            <input type="text" class="form-control rounded-right" id="signup_last_name" placeholder="Surname" v-model="last_name">
+                        </div>
+                    </div>
                     <div class="form-group">
                         <label for="signup_login" class="sr-only"></label>
                         <div class="input-group">
                             <input type="text" class="form-control" id="signup_login" required v-model="login" placeholder="Login">
-                            <span class="input-group-append">
+                            <span class="input-group-append input-group-prepend">
                                 <span class="input-group-text">@</span>
                             </span>
                             <input v-if="is_domain" type="text" class="form-control rounded-right" id="signup_domain" required v-model="domain" placeholder="Domain">
-                            <select v-else class="custom-select rounded-right" id="signup_domain" required v-model="domain"></select>
+                            <select v-else class="custom-select rounded-right" id="signup_domain" required v-model="domain">
+                                <option v-for="domain in domains" :key="domain" :value="domain">{{ domain }}</option>
+                            </select>
                         </div>
                     </div>
                     <div class="form-group">
@@ -88,8 +96,10 @@
                         <label for="signup_voucher" class="sr-only">Voucher code</label>
                         <input type="text" class="form-control" id="signup_voucher" placeholder="Voucher code" v-model="voucher">
                     </div>
-                    <button class="btn btn-secondary" type="button" @click="stepBack">Back</button>
-                    <button class="btn btn-primary" type="submit"><svg-icon icon="check"></svg-icon> Submit</button>
+                    <button v-if="!invitation" class="btn btn-secondary" type="button" @click="stepBack">Back</button>
+                    <button class="btn btn-primary" type="submit">
+                        <svg-icon icon="check"></svg-icon> <span v-if="invitation">Sign Up</span><span v-else>Submit</span>
+                    </button>
                 </form>
             </div>
         </div>
@@ -109,8 +119,10 @@
                 password: '',
                 password_confirmation: '',
                 domain: '',
-                plan: null,
+                domains: [],
+                invitation: null,
                 is_domain: false,
+                plan: null,
                 plan_icons: {
                     individual: 'user',
                     group: 'users'
@@ -122,7 +134,25 @@
         mounted() {
             let param = this.$route.params.param;
 
-            if (param) {
+            if (this.$route.name == 'signup-invite') {
+                this.$root.startLoading()
+                axios.get('/api/auth/signup/invitations/' + param)
+                    .then(response => {
+                        this.invitation = response.data
+                        this.login = response.data.login
+                        this.voucher = response.data.voucher
+                        this.first_name = response.data.first_name
+                        this.last_name = response.data.last_name
+                        this.plan = response.data.plan
+                        this.is_domain = response.data.is_domain
+                        this.setDomain(response.data)
+                        this.$root.stopLoading()
+                        this.displayForm(3, true)
+                    })
+                    .catch(error => {
+                        this.$root.errorHandler(error)
+                    })
+            } else if (param) {
                 if (this.$route.path.indexOf('/signup/voucher/') === 0) {
                     // Voucher (discount) code
                     this.voucher = param
@@ -199,13 +229,7 @@
 
                     // Fill the domain selector with available domains
                     if (!this.is_domain) {
-                        let options = []
-                        $('select#signup_domain').html('')
-                        $.each(response.data.domains, (i, v) => {
-                            options.push($('<option>').text(v).attr('value', v))
-                        })
-                        $('select#signup_domain').append(options)
-                        this.domain = window.config['app.domain']
+                        this.setDomain(response.data)
                     }
                 }).catch(error => {
                     if (bylink === true) {
@@ -219,15 +243,25 @@
             submitStep3() {
                 this.$root.clearFormValidation($('#step3 form'))
 
-                axios.post('/api/auth/signup', {
-                    code: this.code,
-                    short_code: this.short_code,
+                let post = {
                     login: this.login,
                     domain: this.domain,
                     password: this.password,
                     password_confirmation: this.password_confirmation,
                     voucher: this.voucher
-                }).then(response => {
+                }
+
+                if (this.invitation) {
+                    post.invitation = this.invitation.id
+                    post.plan = this.plan
+                    post.first_name = this.first_name
+                    post.last_name = this.last_name
+                } else {
+                    post.code = this.code
+                    post.short_code = this.short_code
+                }
+
+                axios.post('/api/auth/signup', post).then(response => {
                     // auto-login and goto dashboard
                     this.$root.loginUser(response.data)
                 })
@@ -258,6 +292,13 @@
                 if (focus) {
                     $('#step' + step).find('input').first().focus()
                 }
+            },
+            setDomain(response) {
+                if (response.domains) {
+                    this.domains = response.domains
+                }
+
+                this.domain = response.domain || window.config['app.domain']
             }
         }
     }
diff --git a/src/routes/api.php b/src/routes/api.php
--- a/src/routes/api.php
+++ b/src/routes/api.php
@@ -45,8 +45,9 @@
         Route::post('password-reset/verify', 'API\PasswordResetController@verify');
         Route::post('password-reset', 'API\PasswordResetController@reset');
 
-        Route::get('signup/plans', 'API\SignupController@plans');
         Route::post('signup/init', 'API\SignupController@init');
+        Route::get('signup/invitations/{id}', 'API\SignupController@invitation');
+        Route::get('signup/plans', 'API\SignupController@plans');
         Route::post('signup/verify', 'API\SignupController@verify');
         Route::post('signup', 'API\SignupController@signup');
     }
@@ -172,6 +173,8 @@
         Route::get('domains/{id}/confirm', 'API\V4\Reseller\DomainsController@confirm');
 
         Route::apiResource('entitlements', API\V4\Reseller\EntitlementsController::class);
+        Route::apiResource('invitations', API\V4\Reseller\InvitationsController::class);
+        Route::post('invitations/{id}/resend', 'API\V4\Reseller\InvitationsController@resend');
         Route::apiResource('packages', API\V4\Reseller\PackagesController::class);
         Route::apiResource('skus', API\V4\Reseller\SkusController::class);
         Route::apiResource('users', API\V4\Reseller\UsersController::class);
diff --git a/src/tests/Browser/Pages/Reseller/Invitations.php b/src/tests/Browser/Pages/Reseller/Invitations.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Browser/Pages/Reseller/Invitations.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace Tests\Browser\Pages\Reseller;
+
+use Laravel\Dusk\Page;
+
+class Invitations extends Page
+{
+    /**
+     * Get the URL for the page.
+     *
+     * @return string
+     */
+    public function url(): string
+    {
+        return '/invitations';
+    }
+
+    /**
+     * Assert that the browser is on the page.
+     *
+     * @param \Laravel\Dusk\Browser $browser The browser object
+     *
+     * @return void
+     */
+    public function assert($browser)
+    {
+        $browser->assertPathIs($this->url())
+            ->waitUntilMissing('@app .app-loader')
+            ->assertSeeIn('#invitations .card-title', 'Signup Invitations');
+    }
+
+    /**
+     * Get the element shortcuts for the page.
+     *
+     * @return array
+     */
+    public function elements(): array
+    {
+        return [
+            '@app' => '#app',
+            '@create-button' => '.card-text button.create-invite',
+            '@create-dialog' => '#invite-create',
+            '@search-button' => '#search-form button',
+            '@search-input' => '#search-form input',
+            '@table' => '#invitations-list',
+        ];
+    }
+}
diff --git a/src/tests/Browser/Reseller/InvitationsTest.php b/src/tests/Browser/Reseller/InvitationsTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Browser/Reseller/InvitationsTest.php
@@ -0,0 +1,222 @@
+<?php
+
+namespace Tests\Browser\Reseller;
+
+use App\SignupInvitation;
+use Illuminate\Support\Facades\Queue;
+use Tests\Browser;
+use Tests\Browser\Components\Dialog;
+use Tests\Browser\Components\Menu;
+use Tests\Browser\Components\Toast;
+use Tests\Browser\Pages\Dashboard;
+use Tests\Browser\Pages\Home;
+use Tests\Browser\Pages\Reseller\Invitations;
+use Tests\TestCaseDusk;
+
+class InvitationsTest extends TestCaseDusk
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+        self::useResellerUrl();
+        SignupInvitation::truncate();
+    }
+
+    /**
+     * Test invitations page (unauthenticated)
+     */
+    public function testInvitationsUnauth(): void
+    {
+        // Test that the page requires authentication
+        $this->browse(function (Browser $browser) {
+            $browser->visit('/invitations')->on(new Home());
+        });
+    }
+
+    /**
+     * Test Invitations creation
+     */
+    public function testInvitationCreate(): void
+    {
+        $this->browse(function (Browser $browser) {
+            $date_regexp = '/^20[0-9]{2}-/';
+
+            $browser->visit(new Home())
+                ->submitLogon('reseller@kolabnow.com', 'reseller', true)
+                ->on(new Dashboard())
+                ->assertSeeIn('@links .link-invitations', 'Invitations')
+                ->click('@links .link-invitations')
+                ->on(new Invitations())
+                ->assertElementsCount('@table tbody tr', 0)
+                ->assertMissing('#more-loader')
+                ->assertSeeIn('@table tfoot td', "There are no invitations in the database.")
+                ->assertSeeIn('@create-button', 'Create invite(s)');
+
+            // Create a single invite with email address input
+            $browser->click('@create-button')
+                ->with(new Dialog('#invite-create'), function (Browser $browser) {
+                    $browser->assertSeeIn('@title', 'Invite for a signup')
+                        ->assertFocused('@body input#email')
+                        ->assertValue('@body input#email', '')
+                        ->type('@body input#email', 'test')
+                        ->assertSeeIn('@button-action', 'Send invite(s)')
+                        ->click('@button-action')
+                        ->assertToast(Toast::TYPE_ERROR, "Form validation error")
+                        ->waitFor('@body input#email.is-invalid')
+                        ->assertSeeIn(
+                            '@body input#email.is-invalid + .invalid-feedback',
+                            "The email must be a valid email address."
+                        )
+                        ->type('@body input#email', 'test@domain.tld')
+                        ->click('@button-action');
+                })
+                ->assertToast(Toast::TYPE_SUCCESS, "The invitation has been created.")
+                ->waitUntilMissing('#invite-create')
+                ->waitUntilMissing('@table .app-loader')
+                ->assertElementsCount('@table tbody tr', 1)
+                ->assertMissing('@table tfoot')
+                ->assertSeeIn('@table tbody tr td.email', 'test@domain.tld')
+                ->assertText('@table tbody tr td.email title', 'Not sent yet')
+                ->assertTextRegExp('@table tbody tr td.datetime', $date_regexp)
+                ->assertVisible('@table tbody tr td.buttons button.button-delete')
+                ->assertVisible('@table tbody tr td.buttons button.button-resend:disabled');
+
+            sleep(1);
+
+            // Create invites from a file
+            $browser->click('@create-button')
+                ->with(new Dialog('#invite-create'), function (Browser $browser) {
+                    $browser->assertFocused('@body input#email')
+                        ->assertValue('@body input#email', '')
+                        ->assertMissing('@body input#email.is-invalid')
+                        // Submit an empty file
+                        ->attach('@body input#file', __DIR__ . '/../../data/empty.csv')
+                        ->assertSeeIn('@body input#file + label', 'empty.csv')
+                        ->click('@button-action')
+                        ->assertToast(Toast::TYPE_ERROR, "Form validation error")
+                        // ->waitFor('input#file.is-invalid')
+                        ->assertSeeIn(
+                            '@body input#file.is-invalid + label + .invalid-feedback',
+                            "Failed to find any valid email addresses in the uploaded file."
+                        )
+                        // Submit non-empty file
+                        ->attach('@body input#file', __DIR__ . '/../../data/email.csv')
+                        ->click('@button-action');
+                })
+                ->assertToast(Toast::TYPE_SUCCESS, "2 invitations has been created.")
+                ->waitUntilMissing('#invite-create')
+                ->waitUntilMissing('@table .app-loader')
+                ->assertElementsCount('@table tbody tr', 3)
+                ->assertTextRegExp('@table tbody tr:nth-child(1) td.email', '/email[12]@test\.com$/')
+                ->assertTextRegExp('@table tbody tr:nth-child(2) td.email', '/email[12]@test\.com$/');
+        });
+    }
+
+    /**
+     * Test Invitations deletion and resending
+     */
+    public function testInvitationDeleteAndResend(): void
+    {
+        $this->browse(function (Browser $browser) {
+            Queue::fake();
+            $i1 = SignupInvitation::create(['email' => 'test1@domain.org']);
+            $i2 = SignupInvitation::create(['email' => 'test2@domain.org']);
+            SignupInvitation::where('id', $i2->id)
+                ->update(['created_at' => now()->subHours('2'), 'status' => SignupInvitation::STATUS_FAILED]);
+
+            // Test deleting
+            $browser->visit(new Invitations())
+                // ->submitLogon('reseller@kolabnow.com', 'reseller', true)
+                ->assertElementsCount('@table tbody tr', 2)
+                ->click('@table tbody tr:first-child button.button-delete')
+                ->assertToast(Toast::TYPE_SUCCESS, "Invitation deleted successfully.")
+                ->assertElementsCount('@table tbody tr', 1);
+
+            // Test resending
+            $browser->click('@table tbody tr:first-child button.button-resend')
+                ->assertToast(Toast::TYPE_SUCCESS, "Invitation added to the sending queue successfully.")
+                ->assertElementsCount('@table tbody tr', 1);
+        });
+    }
+
+    /**
+     * Test Invitations list (paging and searching)
+     */
+    public function testInvitationsList(): void
+    {
+        $this->browse(function (Browser $browser) {
+            Queue::fake();
+            $i1 = SignupInvitation::create(['email' => 'email1@ext.com']);
+            $i2 = SignupInvitation::create(['email' => 'email2@ext.com']);
+            $i3 = SignupInvitation::create(['email' => 'email3@ext.com']);
+            $i4 = SignupInvitation::create(['email' => 'email4@other.com']);
+            $i5 = SignupInvitation::create(['email' => 'email5@other.com']);
+            $i6 = SignupInvitation::create(['email' => 'email6@other.com']);
+            $i7 = SignupInvitation::create(['email' => 'email7@other.com']);
+            $i8 = SignupInvitation::create(['email' => 'email8@other.com']);
+            $i9 = SignupInvitation::create(['email' => 'email9@other.com']);
+            $i10 = SignupInvitation::create(['email' => 'email10@other.com']);
+            $i11 = SignupInvitation::create(['email' => 'email11@other.com']);
+
+            SignupInvitation::query()->update(['created_at' => now()->subDays('1')]);
+            SignupInvitation::where('id', $i1->id)
+                ->update(['created_at' => now()->subHours('2'), 'status' => SignupInvitation::STATUS_FAILED]);
+            SignupInvitation::where('id', $i2->id)
+                ->update(['created_at' => now()->subHours('3'), 'status' => SignupInvitation::STATUS_SENT]);
+            SignupInvitation::where('id', $i3->id)
+                ->update(['created_at' => now()->subHours('4'), 'status' => SignupInvitation::STATUS_COMPLETED]);
+            SignupInvitation::where('id', $i11->id)->update(['created_at' => now()->subDays('3')]);
+
+            // Test paging (load more) feature
+            $browser->visit(new Invitations())
+                // ->submitLogon('reseller@kolabnow.com', 'reseller', true)
+                ->assertElementsCount('@table tbody tr', 10)
+                ->assertSeeIn('#more-loader button', 'Load more')
+                ->with('@table tbody', function ($browser) use ($i1, $i2, $i3) {
+                    $browser->assertSeeIn('tr:nth-child(1) td.email', $i1->email)
+                        ->assertText('tr:nth-child(1) td.email svg.text-danger title', 'Sending failed')
+                        ->assertVisible('tr:nth-child(1) td.buttons button.button-delete')
+                        ->assertVisible('tr:nth-child(1) td.buttons button.button-resend:not(:disabled)')
+                        ->assertSeeIn('tr:nth-child(2) td.email', $i2->email)
+                        ->assertText('tr:nth-child(2) td.email svg.text-primary title', 'Sent')
+                        ->assertVisible('tr:nth-child(2) td.buttons button.button-delete')
+                        ->assertVisible('tr:nth-child(2) td.buttons button.button-resend:not(:disabled)')
+                        ->assertSeeIn('tr:nth-child(3) td.email', $i3->email)
+                        ->assertText('tr:nth-child(3) td.email svg.text-success title', 'User signed up')
+                        ->assertVisible('tr:nth-child(3) td.buttons button.button-delete')
+                        ->assertVisible('tr:nth-child(3) td.buttons button.button-resend:disabled')
+                        ->assertText('tr:nth-child(4) td.email svg title', 'Not sent yet')
+                        ->assertVisible('tr:nth-child(4) td.buttons button.button-delete')
+                        ->assertVisible('tr:nth-child(4) td.buttons button.button-resend:disabled');
+                })
+                ->click('#more-loader button')
+                ->whenAvailable('@table tbody tr:nth-child(11)', function ($browser) use ($i11) {
+                    $browser->assertSeeIn('td.email', $i11->email);
+                })
+                ->assertMissing('#more-loader button');
+
+            // Test searching (by domain)
+            $browser->type('@search-input', 'ext.com')
+                ->click('@search-button')
+                ->waitUntilMissing('@table .app-loader')
+                ->assertElementsCount('@table tbody tr', 3)
+                ->assertMissing('#more-loader button')
+                // search by full email
+                ->type('@search-input', 'email7@other.com')
+                ->keys('@search-input', '{enter}')
+                ->waitUntilMissing('@table .app-loader')
+                ->assertElementsCount('@table tbody tr', 1)
+                ->assertSeeIn('@table tbody tr:nth-child(1) td.email', 'email7@other.com')
+                ->assertMissing('#more-loader button')
+                // reset search
+                ->vueClear('#search-form input')
+                ->keys('@search-input', '{enter}')
+                ->waitUntilMissing('@table .app-loader')
+                ->assertElementsCount('@table tbody tr', 10)
+                ->assertVisible('#more-loader button');
+        });
+    }
+}
diff --git a/src/tests/Browser/SignupTest.php b/src/tests/Browser/SignupTest.php
--- a/src/tests/Browser/SignupTest.php
+++ b/src/tests/Browser/SignupTest.php
@@ -5,6 +5,7 @@
 use App\Discount;
 use App\Domain;
 use App\SignupCode;
+use App\SignupInvitation;
 use App\User;
 use Tests\Browser;
 use Tests\Browser\Components\Menu;
@@ -28,11 +29,15 @@
         $this->deleteTestDomain('user-domain-signup.com');
     }
 
+    /**
+     * {@inheritDoc}
+     */
     public function tearDown(): void
     {
         $this->deleteTestUser('signuptestdusk@' . \config('app.domain'));
         $this->deleteTestUser('admin@user-domain-signup.com');
         $this->deleteTestDomain('user-domain-signup.com');
+        SignupInvitation::truncate();
 
         parent::tearDown();
     }
@@ -294,17 +299,22 @@
 
             // Here we expect 3 text inputs, Back and Continue buttons
             $browser->with('@step3', function ($step) {
-                $step->assertVisible('#signup_login');
-                $step->assertVisible('#signup_password');
-                $step->assertVisible('#signup_confirm');
-                $step->assertVisible('select#signup_domain');
-                $step->assertVisible('[type=button]');
-                $step->assertVisible('[type=submit]');
-                $step->assertFocused('#signup_login');
-                $step->assertValue('select#signup_domain', \config('app.domain'));
-                $step->assertValue('#signup_login', '');
-                $step->assertValue('#signup_password', '');
-                $step->assertValue('#signup_confirm', '');
+                $step->assertSeeIn('.card-title', 'Sign Up - Step 3/3')
+                    ->assertMissing('#signup_last_name')
+                    ->assertMissing('#signup_first_name')
+                    ->assertVisible('#signup_login')
+                    ->assertVisible('#signup_password')
+                    ->assertVisible('#signup_confirm')
+                    ->assertVisible('select#signup_domain')
+                    ->assertElementsCount('select#signup_domain option', 13, false)
+                    ->assertVisible('[type=button]')
+                    ->assertVisible('[type=submit]')
+                    ->assertSeeIn('[type=submit]', 'Submit')
+                    ->assertFocused('#signup_login')
+                    ->assertValue('select#signup_domain', \config('app.domain'))
+                    ->assertValue('#signup_login', '')
+                    ->assertValue('#signup_password', '')
+                    ->assertValue('#signup_confirm', '');
 
                 // TODO: Test domain selector
             });
@@ -542,4 +552,83 @@
         $discount = Discount::where('code', 'TEST')->first();
         $this->assertSame($discount->id, $user->wallets()->first()->discount_id);
     }
+
+    /**
+     * Test signup via invitation link
+     */
+    public function testSignupInvitation(): void
+    {
+        // Test non-existing invitation
+        $this->browse(function (Browser $browser) {
+            $browser->visit('/signup/invite/TEST')
+                ->onWithoutAssert(new Signup())
+                ->waitFor('#app > #error-page')
+                ->assertErrorPage(404);
+        });
+
+        $invitation = SignupInvitation::create(['email' => 'test@domain.org']);
+
+        $this->browse(function (Browser $browser) use ($invitation) {
+            $browser->visit('/signup/invite/' . $invitation->id)
+                ->onWithoutAssert(new Signup())
+                ->waitUntilMissing('.app-loader')
+                ->with('@step3', function ($step) {
+                    $step->assertMissing('.card-title')
+                        ->assertVisible('#signup_last_name')
+                        ->assertVisible('#signup_first_name')
+                        ->assertVisible('#signup_login')
+                        ->assertVisible('#signup_password')
+                        ->assertVisible('#signup_confirm')
+                        ->assertVisible('select#signup_domain')
+                        ->assertElementsCount('select#signup_domain option', 13, false)
+                        ->assertVisible('[type=submit]')
+                        ->assertMissing('[type=button]') // Back button
+                        ->assertSeeIn('[type=submit]', 'Sign Up')
+                        ->assertFocused('#signup_first_name')
+                        ->assertValue('select#signup_domain', \config('app.domain'))
+                        ->assertValue('#signup_first_name', '')
+                        ->assertValue('#signup_last_name', '')
+                        ->assertValue('#signup_login', '')
+                        ->assertValue('#signup_password', '')
+                        ->assertValue('#signup_confirm', '');
+
+                    // Submit invalid data
+                    $step->type('#signup_login', '*')
+                        ->type('#signup_password', '12345678')
+                        ->type('#signup_confirm', '123456789')
+                        ->click('[type=submit]')
+                        ->waitFor('#signup_login.is-invalid')
+                        ->assertVisible('#signup_domain + .invalid-feedback')
+                        ->assertVisible('#signup_password.is-invalid')
+                        ->assertVisible('#signup_password + .invalid-feedback')
+                        ->assertFocused('#signup_login')
+                        ->assertToast(Toast::TYPE_ERROR, 'Form validation error');
+
+                    // Submit valid data
+                    $step->type('#signup_confirm', '12345678')
+                        ->type('#signup_login', 'signuptestdusk')
+                        ->type('#signup_first_name', 'First')
+                        ->type('#signup_last_name', 'Last')
+                        ->click('[type=submit]');
+                })
+                // At this point we should be auto-logged-in to dashboard
+                ->waitUntilMissing('@step3')
+                ->waitUntilMissing('.app-loader')
+                ->on(new Dashboard())
+                ->assertUser('signuptestdusk@' . \config('app.domain'))
+                // Logout the user
+                ->within(new Menu(), function ($browser) {
+                    $browser->clickMenuItem('logout');
+                });
+        });
+
+        $invitation->refresh();
+        $user = User::where('email', 'signuptestdusk@' . \config('app.domain'))->first();
+
+        $this->assertTrue($invitation->isCompleted());
+        $this->assertSame($user->id, $invitation->user_id);
+        $this->assertSame('First', $user->getSetting('first_name'));
+        $this->assertSame('Last', $user->getSetting('last_name'));
+        $this->assertSame($invitation->email, $user->getSetting('external_email'));
+    }
 }
diff --git a/src/tests/Feature/Controller/Reseller/InvitationsTest.php b/src/tests/Feature/Controller/Reseller/InvitationsTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Feature/Controller/Reseller/InvitationsTest.php
@@ -0,0 +1,348 @@
+<?php
+
+namespace Tests\Feature\Controller\Reseller;
+
+use App\SignupInvitation;
+use App\Tenant;
+use Illuminate\Http\Testing\File;
+use Illuminate\Support\Facades\Queue;
+use Tests\TestCase;
+
+class InvitationsTest extends TestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        SignupInvitation::truncate();
+
+        self::useResellerUrl();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function tearDown(): void
+    {
+        SignupInvitation::truncate();
+
+        \config(['app.tenant_id' => 1]);
+
+        parent::tearDown();
+    }
+
+    /**
+     * Test deleting invitations (DELETE /api/v4/invitations/<id>)
+     */
+    public function testDestroy(): void
+    {
+        Queue::fake();
+
+        $user = $this->getTestUser('john@kolab.org');
+        $admin = $this->getTestUser('jeroen@jeroen.jeroen');
+        $reseller = $this->getTestUser('reseller@reseller.com');
+        $reseller2 = $this->getTestUser('reseller@kolabnow.com');
+        $tenant = Tenant::where('title', 'Sample Tenant')->first();
+
+        \config(['app.tenant_id' => $tenant->id]);
+
+        $inv = SignupInvitation::create(['email' => 'email1@ext.com']);
+
+        // Non-admin user
+        $response = $this->actingAs($user)->delete("api/v4/invitations/{$inv->id}");
+        $response->assertStatus(403);
+
+        // Admin user
+        $response = $this->actingAs($admin)->delete("api/v4/invitations/{$inv->id}");
+        $response->assertStatus(403);
+
+        // Reseller user, but different tenant
+        $response = $this->actingAs($reseller2)->delete("api/v4/invitations/{$inv->id}");
+        $response->assertStatus(403);
+
+        // Reseller - non-existing invitation identifier
+        $response = $this->actingAs($reseller)->delete("api/v4/invitations/abd");
+        $response->assertStatus(404);
+
+        // Reseller - existing invitation
+        $response = $this->actingAs($reseller)->delete("api/v4/invitations/{$inv->id}");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame('success', $json['status']);
+        $this->assertSame("Invitation deleted successfully.", $json['message']);
+        $this->assertSame(null, SignupInvitation::find($inv->id));
+    }
+
+    /**
+     * Test listing invitations (GET /api/v4/invitations)
+     */
+    public function testIndex(): void
+    {
+        Queue::fake();
+
+        $user = $this->getTestUser('john@kolab.org');
+        $admin = $this->getTestUser('jeroen@jeroen.jeroen');
+        $reseller = $this->getTestUser('reseller@reseller.com');
+        $reseller2 = $this->getTestUser('reseller@kolabnow.com');
+        $tenant = Tenant::where('title', 'Sample Tenant')->first();
+
+        \config(['app.tenant_id' => $tenant->id]);
+
+        // Non-admin user
+        $response = $this->actingAs($user)->get("api/v4/invitations");
+        $response->assertStatus(403);
+
+        // Admin user
+        $response = $this->actingAs($admin)->get("api/v4/invitations");
+        $response->assertStatus(403);
+
+        // Reseller user, but different tenant
+        $response = $this->actingAs($reseller2)->get("api/v4/invitations");
+        $response->assertStatus(403);
+
+        // Reseller (empty list)
+        $response = $this->actingAs($reseller)->get("api/v4/invitations");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame(0, $json['count']);
+        $this->assertSame([], $json['list']);
+        $this->assertSame(1, $json['page']);
+        $this->assertFalse($json['hasMore']);
+
+        // Add some invitations
+        $i1 = SignupInvitation::create(['email' => 'email1@ext.com']);
+        $i2 = SignupInvitation::create(['email' => 'email2@ext.com']);
+        $i3 = SignupInvitation::create(['email' => 'email3@ext.com']);
+        $i4 = SignupInvitation::create(['email' => 'email4@other.com']);
+        $i5 = SignupInvitation::create(['email' => 'email5@other.com']);
+        $i6 = SignupInvitation::create(['email' => 'email6@other.com']);
+        $i7 = SignupInvitation::create(['email' => 'email7@other.com']);
+        $i8 = SignupInvitation::create(['email' => 'email8@other.com']);
+        $i9 = SignupInvitation::create(['email' => 'email9@other.com']);
+        $i10 = SignupInvitation::create(['email' => 'email10@other.com']);
+        $i11 = SignupInvitation::create(['email' => 'email11@other.com']);
+        $i12 = SignupInvitation::create(['email' => 'email12@test.com']);
+        $i13 = SignupInvitation::create(['email' => 'email13@ext.com']);
+
+        SignupInvitation::query()->update(['created_at' => now()->subDays('1')]);
+        SignupInvitation::where('id', $i1->id)
+            ->update(['created_at' => now()->subHours('2'), 'status' => SignupInvitation::STATUS_FAILED]);
+        SignupInvitation::where('id', $i2->id)
+            ->update(['created_at' => now()->subHours('3'), 'status' => SignupInvitation::STATUS_SENT]);
+        SignupInvitation::where('id', $i11->id)->update(['created_at' => now()->subDays('3')]);
+        SignupInvitation::where('id', $i12->id)->update(['tenant_id' => 1]);
+        SignupInvitation::where('id', $i13->id)->update(['tenant_id' => 1]);
+
+        $response = $this->actingAs($reseller)->get("api/v4/invitations");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame(10, $json['count']);
+        $this->assertSame(1, $json['page']);
+        $this->assertTrue($json['hasMore']);
+        $this->assertSame($i1->id, $json['list'][0]['id']);
+        $this->assertSame($i1->email, $json['list'][0]['email']);
+        $this->assertSame(true, $json['list'][0]['isFailed']);
+        $this->assertSame(false, $json['list'][0]['isNew']);
+        $this->assertSame(false, $json['list'][0]['isSent']);
+        $this->assertSame(false, $json['list'][0]['isCompleted']);
+        $this->assertSame($i2->id, $json['list'][1]['id']);
+        $this->assertSame($i2->email, $json['list'][1]['email']);
+        $this->assertFalse(in_array($i12->email, array_column($json['list'], 'email')));
+        $this->assertFalse(in_array($i13->email, array_column($json['list'], 'email')));
+
+        $response = $this->actingAs($reseller)->get("api/v4/invitations?page=2");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame(1, $json['count']);
+        $this->assertSame(2, $json['page']);
+        $this->assertFalse($json['hasMore']);
+        $this->assertSame($i11->id, $json['list'][0]['id']);
+
+        // Test searching (email address)
+        $response = $this->actingAs($reseller)->get("api/v4/invitations?search=email3@ext.com");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame(1, $json['count']);
+        $this->assertSame(1, $json['page']);
+        $this->assertFalse($json['hasMore']);
+        $this->assertSame($i3->id, $json['list'][0]['id']);
+
+        // Test searching (domain)
+        $response = $this->actingAs($reseller)->get("api/v4/invitations?search=ext.com");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame(3, $json['count']);
+        $this->assertSame(1, $json['page']);
+        $this->assertFalse($json['hasMore']);
+        $this->assertSame($i1->id, $json['list'][0]['id']);
+    }
+
+    /**
+     * Test resending invitations (POST /api/v4/invitations/<id>/resend)
+     */
+    public function testResend(): void
+    {
+        Queue::fake();
+
+        $user = $this->getTestUser('john@kolab.org');
+        $admin = $this->getTestUser('jeroen@jeroen.jeroen');
+        $reseller = $this->getTestUser('reseller@reseller.com');
+        $reseller2 = $this->getTestUser('reseller@kolabnow.com');
+        $tenant = Tenant::where('title', 'Sample Tenant')->first();
+
+        \config(['app.tenant_id' => $tenant->id]);
+
+        $inv = SignupInvitation::create(['email' => 'email1@ext.com']);
+        SignupInvitation::where('id', $inv->id)->update(['status' => SignupInvitation::STATUS_FAILED]);
+
+        // Non-admin user
+        $response = $this->actingAs($user)->post("api/v4/invitations/{$inv->id}/resend");
+        $response->assertStatus(403);
+
+        // Admin user
+        $response = $this->actingAs($admin)->post("api/v4/invitations/{$inv->id}/resend");
+        $response->assertStatus(403);
+
+        // Reseller user, but different tenant
+        $response = $this->actingAs($reseller2)->post("api/v4/invitations/{$inv->id}/resend");
+        $response->assertStatus(403);
+
+        // Reseller - non-existing invitation identifier
+        $response = $this->actingAs($reseller)->post("api/v4/invitations/abd/resend");
+        $response->assertStatus(404);
+
+        // Reseller - existing invitation
+        $response = $this->actingAs($reseller)->post("api/v4/invitations/{$inv->id}/resend");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame('success', $json['status']);
+        $this->assertSame("Invitation added to the sending queue successfully.", $json['message']);
+        $this->assertTrue($inv->fresh()->isNew());
+    }
+
+    /**
+     * Test creating invitations (POST /api/v4/invitations)
+     */
+    public function testStore(): void
+    {
+        Queue::fake();
+
+        $user = $this->getTestUser('john@kolab.org');
+        $admin = $this->getTestUser('jeroen@jeroen.jeroen');
+        $reseller = $this->getTestUser('reseller@reseller.com');
+        $reseller2 = $this->getTestUser('reseller@kolabnow.com');
+        $tenant = Tenant::where('title', 'Sample Tenant')->first();
+
+        \config(['app.tenant_id' => $tenant->id]);
+
+        // Non-admin user
+        $response = $this->actingAs($user)->post("api/v4/invitations", []);
+        $response->assertStatus(403);
+
+        // Admin user
+        $response = $this->actingAs($admin)->post("api/v4/invitations", []);
+        $response->assertStatus(403);
+
+        // Reseller user, but different tenant
+        $response = $this->actingAs($reseller2)->post("api/v4/invitations", []);
+        $response->assertStatus(403);
+
+        // Reseller (empty post)
+        $response = $this->actingAs($reseller)->post("api/v4/invitations", []);
+        $response->assertStatus(422);
+
+        $json = $response->json();
+
+        $this->assertSame('error', $json['status']);
+        $this->assertCount(1, $json['errors']);
+        $this->assertSame("The email field is required.", $json['errors']['email'][0]);
+
+        // Invalid email address
+        $post = ['email' => 'test'];
+        $response = $this->actingAs($reseller)->post("api/v4/invitations", $post);
+        $response->assertStatus(422);
+
+        $json = $response->json();
+
+        $this->assertSame('error', $json['status']);
+        $this->assertCount(1, $json['errors']);
+        $this->assertSame("The email must be a valid email address.", $json['errors']['email'][0]);
+
+        // Valid email address
+        $post = ['email' => 'test@external.org'];
+        $response = $this->actingAs($reseller)->post("api/v4/invitations", $post);
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame('success', $json['status']);
+        $this->assertSame("The invitation has been created.", $json['message']);
+        $this->assertSame(1, $json['count']);
+        $this->assertSame(1, SignupInvitation::count());
+
+        // Test file input (empty file)
+        $tmpfile = tmpfile();
+        fwrite($tmpfile, "");
+        $file = new File('test.csv', $tmpfile);
+        $post = ['file' => $file];
+        $response = $this->actingAs($reseller)->post("api/v4/invitations", $post);
+
+        fclose($tmpfile);
+
+        $response->assertStatus(422);
+        $json = $response->json();
+
+        $this->assertSame('error', $json['status']);
+        $this->assertSame("Failed to find any valid email addresses in the uploaded file.", $json['errors']['file']);
+
+        // Test file input with an invalid email address
+        $tmpfile = tmpfile();
+        fwrite($tmpfile, "t1@domain.tld\r\nt2@domain");
+        $file = new File('test.csv', $tmpfile);
+        $post = ['file' => $file];
+        $response = $this->actingAs($reseller)->post("api/v4/invitations", $post);
+
+        fclose($tmpfile);
+
+        $response->assertStatus(422);
+        $json = $response->json();
+
+        $this->assertSame('error', $json['status']);
+        $this->assertSame("Found an invalid email address (t2@domain) on line 2.", $json['errors']['file']);
+
+        // Test file input (two addresses)
+        $tmpfile = tmpfile();
+        fwrite($tmpfile, "t1@domain.tld\r\nt2@domain.tld");
+        $file = new File('test.csv', $tmpfile);
+        $post = ['file' => $file];
+        $response = $this->actingAs($reseller)->post("api/v4/invitations", $post);
+
+        fclose($tmpfile);
+
+        $response->assertStatus(200);
+        $json = $response->json();
+
+        $this->assertSame(1, SignupInvitation::where('email', 't1@domain.tld')->count());
+        $this->assertSame(1, SignupInvitation::where('email', 't2@domain.tld')->count());
+        $this->assertSame('success', $json['status']);
+        $this->assertSame("2 invitations has been created.", $json['message']);
+        $this->assertSame(2, $json['count']);
+    }
+}
diff --git a/src/tests/Feature/Controller/SignupTest.php b/src/tests/Feature/Controller/SignupTest.php
--- a/src/tests/Feature/Controller/SignupTest.php
+++ b/src/tests/Feature/Controller/SignupTest.php
@@ -6,6 +6,7 @@
 use App\Discount;
 use App\Domain;
 use App\SignupCode;
+use App\SignupInvitation as SI;
 use App\User;
 use Illuminate\Support\Facades\Queue;
 use Tests\TestCase;
@@ -28,11 +29,13 @@
         $this->deleteTestUser("SignupControllerTest1@$this->domain");
         $this->deleteTestUser("signuplogin@$this->domain");
         $this->deleteTestUser("admin@external.com");
+        $this->deleteTestUser("test-inv@kolabnow.com");
 
         $this->deleteTestDomain('external.com');
         $this->deleteTestDomain('signup-domain.com');
 
         $this->deleteTestGroup('group-test@kolabnow.com');
+        SI::truncate();
     }
 
     /**
@@ -43,11 +46,13 @@
         $this->deleteTestUser("SignupControllerTest1@$this->domain");
         $this->deleteTestUser("signuplogin@$this->domain");
         $this->deleteTestUser("admin@external.com");
+        $this->deleteTestUser("test-inv@kolabnow.com");
 
         $this->deleteTestDomain('external.com');
         $this->deleteTestDomain('signup-domain.com');
 
         $this->deleteTestGroup('group-test@kolabnow.com');
+        SI::truncate();
 
         parent::tearDown();
     }
@@ -77,10 +82,8 @@
 
     /**
      * Test fetching plans for signup
-     *
-     * @return void
      */
-    public function testSignupPlans()
+    public function testSignupPlans(): void
     {
         $response = $this->get('/api/auth/signup/plans');
         $json = $response->json();
@@ -95,12 +98,37 @@
         $this->assertArrayHasKey('button', $json['plans'][0]);
     }
 
+    /**
+     * Test fetching invitation
+     */
+    public function testSignupInvitations(): void
+    {
+        Queue::fake();
+
+        $invitation = SI::create(['email' => 'email1@ext.com']);
+
+        // Test existing invitation
+        $response = $this->get("/api/auth/signup/invitations/{$invitation->id}");
+        $response->assertStatus(200);
+
+        $json = $response->json();
+
+        $this->assertSame($invitation->id, $json['id']);
+
+        // Test non-existing invitation
+        $response = $this->get("/api/auth/signup/invitations/abc");
+        $response->assertStatus(404);
+
+        // Test completed invitation
+        SI::where('id', $invitation->id)->update(['status' => SI::STATUS_COMPLETED]);
+        $response = $this->get("/api/auth/signup/invitations/{$invitation->id}");
+        $response->assertStatus(404);
+    }
+
     /**
      * Test signup initialization with invalid input
-     *
-     * @return void
      */
-    public function testSignupInitInvalidInput()
+    public function testSignupInitInvalidInput(): void
     {
         // Empty input data
         $data = [];
@@ -167,10 +195,8 @@
 
     /**
      * Test signup initialization with valid input
-     *
-     * @return array
      */
-    public function testSignupInitValidInput()
+    public function testSignupInitValidInput(): array
     {
         Queue::fake();
 
@@ -243,9 +269,8 @@
      * Test signup code verification with invalid input
      *
      * @depends testSignupInitValidInput
-     * @return void
      */
-    public function testSignupVerifyInvalidInput(array $result)
+    public function testSignupVerifyInvalidInput(array $result): void
     {
         // Empty data
         $data = [];
@@ -293,10 +318,8 @@
      * Test signup code verification with valid input
      *
      * @depends testSignupInitValidInput
-     *
-     * @return array
      */
-    public function testSignupVerifyValidInput(array $result)
+    public function testSignupVerifyValidInput(array $result): array
     {
         $code = SignupCode::find($result['code']);
         $data = [
@@ -324,9 +347,8 @@
      * Test last signup step with invalid input
      *
      * @depends testSignupVerifyValidInput
-     * @return void
      */
-    public function testSignupInvalidInput(array $result)
+    public function testSignupInvalidInput(array $result): void
     {
         // Empty data
         $data = [];
@@ -456,9 +478,8 @@
      * Test last signup step with valid input (user creation)
      *
      * @depends testSignupVerifyValidInput
-     * @return void
      */
-    public function testSignupValidInput(array $result)
+    public function testSignupValidInput(array $result): void
     {
         $queue = Queue::fake();
 
@@ -520,10 +541,8 @@
 
     /**
      * Test signup for a group (custom domain) account
-     *
-     * @return void
      */
-    public function testSignupGroupAccount()
+    public function testSignupGroupAccount(): void
     {
         Queue::fake();
 
@@ -641,6 +660,59 @@
         // TODO: Check if the access token works
     }
 
+    /**
+     * Test signup via invitation
+     */
+    public function testSignupViaInvitation(): void
+    {
+        Queue::fake();
+
+        $invitation = SI::create(['email' => 'email1@ext.com']);
+
+        $post = [
+            'invitation' => 'abc',
+            'first_name' => 'Signup',
+            'last_name' => 'User',
+            'login' => 'test-inv',
+            'domain' => 'kolabnow.com',
+            'password' => 'test',
+            'password_confirmation' => 'test',
+        ];
+
+        // Test invalid invitation identifier
+        $response = $this->post('/api/auth/signup', $post);
+        $response->assertStatus(404);
+
+        // Test valid input
+        $post['invitation'] = $invitation->id;
+        $response = $this->post('/api/auth/signup', $post);
+        $result = $response->json();
+
+        $response->assertStatus(200);
+        $this->assertSame('success', $result['status']);
+        $this->assertSame('bearer', $result['token_type']);
+        $this->assertTrue(!empty($result['expires_in']) && is_int($result['expires_in']) && $result['expires_in'] > 0);
+        $this->assertNotEmpty($result['access_token']);
+        $this->assertSame('test-inv@kolabnow.com', $result['email']);
+
+        // Check if the user has been created
+        $user = User::where('email', 'test-inv@kolabnow.com')->first();
+
+        $this->assertNotEmpty($user);
+
+        // Check user settings
+        $this->assertSame($invitation->email, $user->getSetting('external_email'));
+        $this->assertSame($post['first_name'], $user->getSetting('first_name'));
+        $this->assertSame($post['last_name'], $user->getSetting('last_name'));
+
+        $invitation->refresh();
+
+        $this->assertSame($user->id, $invitation->user_id);
+        $this->assertTrue($invitation->isCompleted());
+
+        // TODO: Test POST params validation
+    }
+
     /**
      * List of login/domain validation cases for testValidateLogin()
      *
diff --git a/src/tests/Feature/Jobs/SignupInvitationEmailTest.php b/src/tests/Feature/Jobs/SignupInvitationEmailTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Feature/Jobs/SignupInvitationEmailTest.php
@@ -0,0 +1,68 @@
+<?php
+
+namespace Tests\Feature\Jobs;
+
+use App\Jobs\SignupInvitationEmail;
+use App\Mail\SignupInvitation;
+use App\SignupInvitation as SI;
+use Illuminate\Queue\Events\JobFailed;
+use Illuminate\Support\Facades\Mail;
+use Illuminate\Support\Facades\Queue;
+use Tests\TestCase;
+
+class SignupInvitationEmailTest extends TestCase
+{
+    private $invitation;
+
+    /**
+     * {@inheritDoc}
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        Queue::fake();
+
+        $this->invitation = SI::create(['email' => 'SignupInvitationEmailTest@external.com']);
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function tearDown(): void
+    {
+        $this->invitation->delete();
+    }
+
+    /**
+     * Test job handle
+     */
+    public function testSignupInvitationEmailHandle(): void
+    {
+        Mail::fake();
+
+        // Assert that no jobs were pushed...
+        Mail::assertNothingSent();
+
+        $job = new SignupInvitationEmail($this->invitation);
+        $job->handle();
+
+        // Assert the email sending job was pushed once
+        Mail::assertSent(SignupInvitation::class, 1);
+
+        // Assert the mail was sent to the code's email
+        Mail::assertSent(SignupInvitation::class, function ($mail) {
+            return $mail->hasTo($this->invitation->email);
+        });
+
+        $this->assertTrue($this->invitation->isSent());
+    }
+
+    /**
+     * Test job failure handling
+     */
+    public function testSignupInvitationEmailFailure(): void
+    {
+        $this->markTestIncomplete();
+    }
+}
diff --git a/src/tests/Feature/SignupInvitationTest.php b/src/tests/Feature/SignupInvitationTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Feature/SignupInvitationTest.php
@@ -0,0 +1,118 @@
+<?php
+
+namespace Tests\Feature;
+
+use App\SignupInvitation as SI;
+use Illuminate\Support\Facades\Queue;
+use Tests\TestCase;
+
+class SignupInvitationTest extends TestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        SI::truncate();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public function tearDown(): void
+    {
+        SI::truncate();
+
+        parent::tearDown();
+    }
+
+    /**
+     * Test SignupInvitation creation
+     */
+    public function testCreate(): void
+    {
+        Queue::fake();
+
+        $invitation = SI::create(['email' => 'test@domain.org']);
+
+        $this->assertSame('test@domain.org', $invitation->email);
+        $this->assertSame(SI::STATUS_NEW, $invitation->status);
+        $this->assertSame(\config('app.tenant_id'), $invitation->tenant_id);
+        $this->assertTrue(preg_match('/^[a-f0-9-]{36}$/', $invitation->id) > 0);
+
+        Queue::assertPushed(\App\Jobs\SignupInvitationEmail::class, 1);
+
+        Queue::assertPushed(
+            \App\Jobs\SignupInvitationEmail::class,
+            function ($job) use ($invitation) {
+                $inv = TestCase::getObjectProperty($job, 'invitation');
+
+                return $inv->id === $invitation->id && $inv->email === $invitation->email;
+            }
+        );
+
+        $inst = SI::find($invitation->id);
+
+        $this->assertInstanceOf(SI::class, $inst);
+        $this->assertSame($inst->id, $invitation->id);
+        $this->assertSame($inst->email, $invitation->email);
+    }
+
+    /**
+     * Test SignupInvitation update
+     */
+    public function testUpdate(): void
+    {
+        Queue::fake();
+
+        $invitation = SI::create(['email' => 'test@domain.org']);
+
+        Queue::fake();
+
+        // Test that these status changes do not dispatch the email sending job
+        foreach ([SI::STATUS_FAILED, SI::STATUS_SENT, SI::STATUS_COMPLETED, SI::STATUS_NEW] as $status) {
+            $invitation->status = $status;
+            $invitation->save();
+        }
+
+        Queue::assertNothingPushed();
+
+        // SENT -> NEW should resend the invitation
+        SI::where('id', $invitation->id)->update(['status' => SI::STATUS_SENT]);
+        $invitation->refresh();
+        $invitation->status = SI::STATUS_NEW;
+        $invitation->save();
+
+        Queue::assertPushed(\App\Jobs\SignupInvitationEmail::class, 1);
+
+        Queue::assertPushed(
+            \App\Jobs\SignupInvitationEmail::class,
+            function ($job) use ($invitation) {
+                $inv = TestCase::getObjectProperty($job, 'invitation');
+
+                return $inv->id === $invitation->id && $inv->email === $invitation->email;
+            }
+        );
+
+        Queue::fake();
+
+        // FAILED -> NEW should resend the invitation
+        SI::where('id', $invitation->id)->update(['status' => SI::STATUS_FAILED]);
+        $invitation->refresh();
+        $invitation->status = SI::STATUS_NEW;
+        $invitation->save();
+
+        Queue::assertPushed(\App\Jobs\SignupInvitationEmail::class, 1);
+
+        Queue::assertPushed(
+            \App\Jobs\SignupInvitationEmail::class,
+            function ($job) use ($invitation) {
+                $inv = TestCase::getObjectProperty($job, 'invitation');
+
+                return $inv->id === $invitation->id && $inv->email === $invitation->email;
+            }
+        );
+    }
+}
diff --git a/src/tests/Unit/Mail/SignupInvitationTest.php b/src/tests/Unit/Mail/SignupInvitationTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Unit/Mail/SignupInvitationTest.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Tests\Unit\Mail;
+
+use App\Mail\SignupInvitation;
+use App\SignupInvitation as SI;
+use App\Utils;
+use Tests\MailInterceptTrait;
+use Tests\TestCase;
+
+class SignupInvitationTest extends TestCase
+{
+    use MailInterceptTrait;
+
+    /**
+     * Test email content
+     */
+    public function testBuild(): void
+    {
+        $invitation = new SI([
+                'id' => 'abc',
+                'email' => 'test@email',
+        ]);
+
+        $mail = $this->fakeMail(new SignupInvitation($invitation));
+
+        $html = $mail['html'];
+        $plain = $mail['plain'];
+
+        $url = Utils::serviceUrl('/signup/invite/' . $invitation->id);
+        $link = "<a href=\"$url\">$url</a>";
+        $appName = \config('app.name');
+
+        $this->assertMailSubject("$appName Invitation", $mail['message']);
+
+        $this->assertStringStartsWith('<!DOCTYPE html>', $html);
+        $this->assertTrue(strpos($html, $link) > 0);
+        $this->assertTrue(strpos($html, "invited to join $appName") > 0);
+
+        $this->assertStringStartsWith("Hi,", $plain);
+        $this->assertTrue(strpos($plain, "invited to join $appName") > 0);
+        $this->assertTrue(strpos($plain, $url) > 0);
+    }
+}
diff --git a/src/tests/Unit/SignupInvitationTest.php b/src/tests/Unit/SignupInvitationTest.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Unit/SignupInvitationTest.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace Tests\Unit;
+
+use App\SignupInvitation;
+use Tests\TestCase;
+
+class SignupInvitationTest extends TestCase
+{
+    /**
+     * Test is*() methods
+     *
+     * @return void
+     */
+    public function testStatus()
+    {
+        $invitation = new SignupInvitation();
+
+        $statuses = [
+            SignupInvitation::STATUS_NEW,
+            SignupInvitation::STATUS_SENT,
+            SignupInvitation::STATUS_FAILED,
+            SignupInvitation::STATUS_COMPLETED,
+        ];
+
+        foreach ($statuses as $status) {
+            $invitation->status = $status;
+
+            $this->assertSame($status === SignupInvitation::STATUS_NEW, $invitation->isNew());
+            $this->assertSame($status === SignupInvitation::STATUS_SENT, $invitation->isSent());
+            $this->assertSame($status === SignupInvitation::STATUS_FAILED, $invitation->isFailed());
+            $this->assertSame($status === SignupInvitation::STATUS_COMPLETED, $invitation->isCompleted());
+        }
+    }
+}
diff --git a/src/tests/data/email.csv b/src/tests/data/email.csv
new file mode 100644
--- /dev/null
+++ b/src/tests/data/email.csv
@@ -0,0 +1,2 @@
+email1@test.com
+email2@test.com
diff --git a/src/tests/data/empty.csv b/src/tests/data/empty.csv
new file mode 100644