diff --git a/src/app/DataMigrator/Account.php b/src/app/DataMigrator/Account.php
index 06b8fc82..a9678421 100644
--- a/src/app/DataMigrator/Account.php
+++ b/src/app/DataMigrator/Account.php
@@ -1,55 +1,75 @@
 <?php
 
 namespace App\DataMigrator;
 
 /**
  * Data object representing user account on an external service
  */
 class Account
 {
     /** @var string User name (login) */
     public $username;
 
     /** @var string User password */
     public $password;
 
     /** @var string User email address */
     public $email;
 
     /** @var string Full account location URI */
     public $uri;
 
     /** @var string Username for proxy auth */
-    public $proxy_authnz;
+    public $loginas;
 
 
     /**
      * Object constructor
+     *
+     * Input can be a valid URI or "<username>:<password>".
+     * For proxy authentication use: "<loginas>^<username>:<password>"
+     * or "https://service-admin@password:hostname.domain.tld?loginas=user"
+     *
+     * @param string $input Account specification
      */
     public function __construct(string $input)
     {
-        // Input can be a valid URL or "<username>:<password>"
         $url = parse_url($input);
 
+        // Not valid URI, try the other form of input
         if ($url === false || !array_key_exists('user', $url)) {
             list($user, $password) = explode(':', $input, 2);
             $url = ['user' => $user, 'pass' => $password];
+
+            if (strpos($user, '^')) {
+                list($loginas, $url['user']) = explode('^', $user, 2);
+                $url['query'] = 'loginas=' . urlencode($loginas);
+            }
         }
 
         if (isset($url['user'])) {
             $this->username = urldecode($url['user']);
         }
 
         if (isset($url['pass'])) {
             $this->password = urldecode($url['pass']);
         }
 
         if (isset($url['host'])) {
-            $this->uri = $input;
+            $this->uri = preg_replace('/\?.*$/', '', $input);
+        }
+
+        if (isset($url['query'])) {
+            parse_str($url['query'], $params);
+            if (isset($params['loginas'])) {
+                $this->loginas = urldecode($params['loginas']);
+            }
         }
 
-        if (strpos($this->username, '@')) {
+        if (strpos($this->loginas, '@')) {
+            $this->email = $this->loginas;
+        } elseif (strpos($this->username, '@')) {
             $this->email = $this->username;
         }
     }
 }
diff --git a/src/app/DataMigrator/EWS.php b/src/app/DataMigrator/EWS.php
index de5a22b0..a3fbb903 100644
--- a/src/app/DataMigrator/EWS.php
+++ b/src/app/DataMigrator/EWS.php
@@ -1,296 +1,299 @@
 <?php
 
 namespace App\DataMigrator;
 
 use garethp\ews\API;
 use garethp\ews\API\Type;
 
 /**
  * Data migration from Exchange (EWS)
  */
 class EWS
 {
     /** @var garethp\ews\API EWS API object */
     public $api;
 
     /** @var array Supported folder types */
     protected $folder_classes = [
         EWS\Appointment::FOLDER_TYPE,
         EWS\Contact::FOLDER_TYPE,
         EWS\Task::FOLDER_TYPE,
         // TODO: mail and sticky notes are exported as eml files.
         //       We could use imapsync to synchronize mail, but for notes
         //       the only option will be to convert them to Kolab format here
         //       and upload to Kolab via IMAP, I guess
         // EWS\Note::FOLDER_TYPE,
         // EWS\StickyNote::FOLDER_TYPE,
     ];
 
     /** @var array Interal folders to skip */
     protected $folder_exceptions = [
         'Sharing',
         'Outbox',
         'Calendar/United States holidays',
         'ExternalContacts',
         'AllContacts',
         'AllPersonMetadata',
         'Document Centric Conversations',
         'Favorites',
         'GraphFilesAndWorkingSetSearchFolder',
         'My Contacts',
         'MyContactsExtended',
         'PersonMetadata',
         'People I Know',
         'RelevantContacts',
         'SharedFilesSearchFolder',
         'To-Do Search',
         'UserCuratedContacts',
         'XrmActivityStreamSearch',
         'XrmCompanySearch',
         'XrmDealSearch',
         'XrmSearch',
         'Folder Memberships',
         'Orion Notes',
     ];
 
     /** @var array Map of EWS folder types to Kolab types */
     protected $type_map = [
         EWS\Appointment::FOLDER_TYPE => DAVClient::TYPE_EVENT,
         EWS\Contact::FOLDER_TYPE => DAVClient::TYPE_CONTACT,
         EWS\Task::FOLDER_TYPE => DAVClient::TYPE_TASK,
     ];
 
     /** @var string Output location */
     protected $location;
 
     /** @var Account Source account */
     protected $source;
 
     /** @var Account Destination account */
     protected $destination;
 
     /** @var DAVClient Data importer */
     protected $importer;
 
 
     /**
      * Print progress/debug information
      */
     public function debug($line)
     {
         // TODO: When not in console mode we should
         // not write to stdout, but to log
         $output = new \Symfony\Component\Console\Output\ConsoleOutput;
         $output->writeln($line);
     }
 
     /**
      * Return destination account
      */
     public function getDestination()
     {
         return $this->destination;
     }
 
     /**
      * Return source account
      */
     public function getSource()
     {
         return $this->source;
     }
 
     /**
      * Execute migration for the specified user
      */
     public function migrate(Account $source, Account $destination, array $options = []): void
     {
         $this->source = $source;
         $this->destination = $destination;
 
         // We'll store output in storage/<username> tree
         $this->location = storage_path('export/') . $source->email;
 
         if (!file_exists($this->location)) {
             mkdir($this->location, 0740, true);
         }
 
         // Autodiscover and authenticate the user
-        $this->authenticate($source->username, $source->password);
+        $this->authenticate($source->username, $source->password, $source->loginas);
 
         $this->debug("Logged in. Fetching folders hierarchy...");
 
         $folders = $this->getFolders();
 
         if (empty($options['import-only'])) {
             foreach ($folders as $folder) {
                 $this->debug("Syncing folder {$folder['fullname']}...");
 
                 if ($folder['total'] > 0) {
                     $this->syncItems($folder);
                 }
             }
 
             $this->debug("Done.");
         }
 
         if (empty($options['export-only'])) {
             $this->debug("Importing to Kolab account...");
 
             $this->importer = new DAVClient($destination);
 
             // TODO: If we were to stay with this storage solution and need still
             //       the import mode, it should not require connecting again to
             //       Exchange. Now we do this for simplicity.
             foreach ($folders as $folder) {
                 $this->debug("Syncing folder {$folder['fullname']}...");
 
                 $this->importer->createFolder($folder['fullname'], $folder['type']);
 
                 if ($folder['total'] > 0) {
                     $files = array_diff(scandir($folder['location']), ['.', '..']);
                     foreach ($files as $file) {
                         $this->debug("* Pushing item {$file}...");
                         $this->importer->createObjectFromFile($folder['location'] . '/' . $file, $folder['fullname']);
                         // TODO: remove the file/folder?
                     }
                 }
             }
 
-           $this->debug("Done.");
+            $this->debug("Done.");
         }
     }
 
     /**
      * Autodiscover the server and authenticate the user
      */
-    protected function authenticate(string $user, string $password): void
+    protected function authenticate(string $user, string $password, string $loginas = null): void
     {
         // You should never run the Autodiscover more than once.
         // It can make between 1 and 5 calls before giving up, or before finding your server,
         // depending on how many different attempts it needs to make.
 
         $api = API\ExchangeAutodiscover::getAPI($user, $password);
 
         $server = $api->getClient()->getServer();
         $version = $api->getClient()->getVersion();
+        $options = ['version' => $version];
+
+        if ($loginas) {
+            $options['impersonation'] = $loginas;
+        }
 
         $this->debug("Connected to $server ($version). Authenticating...");
 
-        $this->api = API::withUsernameAndPassword($server, $user, $password, [
-                'version' => $version
-        ]);
+        $this->api = API::withUsernameAndPassword($server, $user, $password, $options);
     }
 
     /**
      * Get folders hierarchy
      */
     protected function getFolders(): array
     {
         // Get full folders hierarchy
         $options = [
             'Traversal' => 'Deep',
         ];
 
         $folders = $this->api->getChildrenFolders('root', $options);
 
         $result = [];
 
         foreach ($folders as $folder) {
             $class = $folder->getFolderClass();
 
             // Skip folder types we do not support
             if (!in_array($class, $this->folder_classes)) {
                 continue;
             }
 
             $name = $fullname = $folder->getDisplayName();
             $id = $folder->getFolderId()->getId();
             $parentId = $folder->getParentFolderId()->getId();
 
             // Create folder name with full path
             if ($parentId && !empty($result[$parentId])) {
                 $fullname = $result[$parentId]['fullname'] . '/' . $name;
             }
 
             // Top-level folder, check if it's a special folder we should ignore
             // FIXME: Is there a better way to distinguish user folders from system ones?
             if (in_array($fullname, $this->folder_exceptions)
                 || strpos($fullname, 'OwaFV15.1All') === 0
             ) {
                 continue;
             }
 
             $result[$id] = [
                 'id' => $folder->getFolderId(),
                 'total' => $folder->getTotalCount(),
                 'class' => $class,
                 'type' => array_key_exists($class, $this->type_map) ? $this->type_map[$class] : null,
                 'name' => $name,
                 'fullname' => $fullname,
                 'location' => $this->location . '/' . $fullname,
             ];
         }
 
         return $result;
     }
 
     /**
      * Synchronize specified folder
      */
     protected function syncItems(array $folder): void
     {
         $request = [
             // Exchange's maximum is 1000
             'IndexedPageItemView' => ['MaxEntriesReturned' => 100, 'Offset' => 0, 'BasePoint' => 'Beginning'],
             'ParentFolderIds' => $folder['id']->toArray(true),
             'Traversal' => 'Shallow',
             'ItemShape' => [
                 'BaseShape' => 'IdOnly',
                 'AdditionalProperties' => [
                     'FieldURI' => ['FieldURI' => 'item:ItemClass'],
                 ],
             ],
         ];
 
         $request = Type::buildFromArray($request);
 
         // Note: It is not possible to get mimeContent with FindItem request
         //       That's why we first get the list of object identifiers and
         //       then call GetItem on each separately.
 
         // TODO: It might be feasible to get all properties for object types
         //       for which we don't use MimeContent, for better performance.
 
         // Request first page
         $response = $this->api->getClient()->FindItem($request);
 
         foreach ($response as $item) {
             $this->syncItem($item, $folder);
         }
 
         // Request other pages until we got all
         while (!$response->isIncludesLastItemInRange()) {
             $response = $this->api->getNextPage($response);
             foreach ($response as $item) {
                 $this->syncItem($item, $folder);
             }
         }
     }
 
     /**
      * Synchronize specified object
      */
     protected function syncItem(Type $item, array $folder): void
     {
         if ($driver = EWS\Item::factory($this, $item, $folder)) {
             $driver->syncItem($item);
             return;
         }
 
         // TODO IPM.Note (email) and IPM.StickyNote
         // Note: iTip messages in mail folders may have different class assigned
         // https://docs.microsoft.com/en-us/office/vba/outlook/Concepts/Forms/item-types-and-message-classes
         $this->debug("Unsupported object type: {$item->getItemClass()}. Skiped.");
     }
 }