diff --git a/src/app/Backends/IMAP.php b/src/app/Backends/IMAP.php
--- a/src/app/Backends/IMAP.php
+++ b/src/app/Backends/IMAP.php
@@ -6,6 +6,7 @@
 use App\Resource;
 use App\SharedFolder;
 use App\User;
+use App\Utils;
 
 class IMAP
 {
@@ -218,14 +219,16 @@
 
         $settings = $resource->getSettings(['invitation_policy', 'folder']);
         $mailbox = self::toUTF7($settings['folder']);
+        $metadata = ['/shared/vendor/kolab/folder-type' => 'event'];
 
-        $acl = null;
+        $acl = [];
         if (!empty($settings['invitation_policy'])) {
             if (preg_match('/^manual:(\S+@\S+)$/', $settings['invitation_policy'], $m)) {
                 $acl = ["{$m[1]}, full"];
             }
         }
-        self::createFolder($imap, $mailbox, false, ['/shared/vendor/kolab/folder-type' => 'event'], $acl);
+
+        self::createFolder($imap, $mailbox, false, $metadata, Utils::ensureAclPostPermission($acl));
 
         $imap->closeConnection();
 
@@ -268,7 +271,8 @@
                 $acl = ["{$m[1]}, full"];
             }
         }
-        self::aclUpdate($imap, $mailbox, $acl);
+
+        self::aclUpdate($imap, $mailbox, Utils::ensureAclPostPermission($acl));
 
         $imap->closeConnection();
 
@@ -316,10 +320,11 @@
         $imap = self::initIMAP($config);
 
         $settings = $folder->getSettings(['acl', 'folder']);
-        $acl = !empty($settings['acl']) ? json_decode($settings['acl'], true) : null;
+        $acl = !empty($settings['acl']) ? json_decode($settings['acl'], true) : [];
         $mailbox = self::toUTF7($settings['folder']);
+        $metadata = ['/shared/vendor/kolab/folder-type' => $folder->type];
 
-        self::createFolder($imap, $mailbox, false, ['/shared/vendor/kolab/folder-type' => $folder->type], $acl);
+        self::createFolder($imap, $mailbox, false, $metadata, Utils::ensureAclPostPermission($acl));
 
         $imap->closeConnection();
 
@@ -359,7 +364,7 @@
         // Note: Shared folder type does not change
 
         // ACL
-        self::aclUpdate($imap, $mailbox, $acl);
+        self::aclUpdate($imap, $mailbox, Utils::ensureAclPostPermission($acl));
 
         $imap->closeConnection();
 
@@ -629,7 +634,7 @@
             throw new \Exception("Failed to create mailbox {$mailbox}");
         }
 
-        if ($acl) {
+        if (!empty($acl)) {
             self::aclUpdate($imap, $mailbox, $acl, true);
         }
 
@@ -656,7 +661,8 @@
         return \collect($acl)
             ->mapWithKeys(function ($item, $key) {
                 list($user, $rights) = explode(',', $item, 2);
-                return [trim($user) => self::ACL_MAP[trim($rights)]];
+                $rights = trim($rights);
+                return [trim($user) => self::ACL_MAP[$rights] ?? $rights];
             })
             ->all();
     }
diff --git a/src/app/Backends/LDAP.php b/src/app/Backends/LDAP.php
--- a/src/app/Backends/LDAP.php
+++ b/src/app/Backends/LDAP.php
@@ -7,6 +7,7 @@
 use App\Resource;
 use App\SharedFolder;
 use App\User;
+use App\Utils;
 
 class LDAP
 {
@@ -1015,7 +1016,7 @@
         $entry['cn'] = $resource->name;
         $entry['owner'] = null;
         $entry['kolabinvitationpolicy'] = null;
-        $entry['acl'] = '';
+        $entry['acl'] = [];
 
         $settings = $resource->getSettings(['invitation_policy', 'folder']);
 
@@ -1044,13 +1045,15 @@
             } elseif (preg_match('/^manual:(\S+@\S+)$/', $settings['invitation_policy'], $m)) {
                 if (self::getUserEntry($ldap, $m[1], $userDN)) {
                     $entry['owner'] = $userDN;
-                    $entry['acl'] = $m[1] . ', full';
+                    $entry['acl'] = [$m[1] . ', full'];
                     $entry['kolabinvitationpolicy'] = 'ACT_MANUAL';
                 } else {
                     $entry['kolabinvitationpolicy'] = 'ACT_ACCEPT';
                 }
             }
         }
+
+        $entry['acl'] = Utils::ensureAclPostPermission($entry['acl']);
     }
 
     /**
@@ -1060,10 +1063,12 @@
     {
         $settings = $folder->getSettings(['acl', 'folder']);
 
+        $acl = !empty($settings['acl']) ? json_decode($settings['acl'], true) : [];
+
         $entry['cn'] = $folder->name;
         $entry['kolabfoldertype'] = $folder->type;
         $entry['kolabtargetfolder'] = $settings['folder'] ?? '';
-        $entry['acl'] = !empty($settings['acl']) ? json_decode($settings['acl'], true) : '';
+        $entry['acl'] = Utils::ensureAclPostPermission($acl);
         $entry['alias'] = $folder->aliases()->pluck('alias')->all();
     }
 
diff --git a/src/app/Utils.php b/src/app/Utils.php
--- a/src/app/Utils.php
+++ b/src/app/Utils.php
@@ -146,6 +146,32 @@
         return strtolower($email);
     }
 
+    /**
+     * Make sure that IMAP folder access rights contains "anyone: p" permission
+     *
+     * @param array $acl ACL (in form of "user, permission" records)
+     *
+     * @return array ACL list
+     */
+    public static function ensureAclPostPermission(array $acl): array
+    {
+        foreach ($acl as $idx => $entry) {
+            if (str_starts_with($entry, 'anyone,')) {
+                if (strpos($entry, 'read-only')) {
+                    $acl[$idx] = 'anyone, lrsp';
+                } elseif (strpos($entry, 'read-write')) {
+                    $acl[$idx] = 'anyone, lrswitednp';
+                }
+
+                return $acl;
+            }
+        }
+
+        $acl[] = 'anyone, p';
+
+        return $acl;
+    }
+
     /**
      * Generate a passphrase. Not intended for use in production, so limited to environments that are not production.
      *
diff --git a/src/tests/Feature/Backends/IMAPTest.php b/src/tests/Feature/Backends/IMAPTest.php
--- a/src/tests/Feature/Backends/IMAPTest.php
+++ b/src/tests/Feature/Backends/IMAPTest.php
@@ -205,10 +205,9 @@
         $this->assertTrue(IMAP::verifySharedFolder($imapFolder = $resource->getSetting('folder')));
 
         $imap = $this->getImap();
-        $expectedAcl = ['john@kolab.org' => str_split('lrswipkxtecdn')];
+        $expectedAcl = ['anyone' => ['p'], 'john@kolab.org' => str_split('lrswipkxtecdn')];
         $acl = $imap->getACL(IMAP::toUTF7($imapFolder));
-        $this->assertTrue(is_array($acl) && isset($acl['john@kolab.org']));
-        $this->assertSame($expectedAcl['john@kolab.org'], $acl['john@kolab.org']);
+        $this->assertSame($expectedAcl, $acl);
 
         // Update the resource (rename)
         $resource->name = 'Resource1 ©' . time();
@@ -219,13 +218,12 @@
         $this->assertTrue($imapFolder != $newImapFolder);
         $this->assertTrue(IMAP::verifySharedFolder($newImapFolder));
         $acl = $imap->getACL(IMAP::toUTF7($newImapFolder));
-        $this->assertTrue(is_array($acl) && isset($acl['john@kolab.org']));
-        $this->assertSame($expectedAcl['john@kolab.org'], $acl['john@kolab.org']);
+        $this->assertSame($expectedAcl, $acl);
 
         // Update the resource (acl change)
         $resource->setSetting('invitation_policy', 'accept');
         $this->assertTrue(IMAP::updateResource($resource));
-        $this->assertSame([], $imap->getACL(IMAP::toUTF7($newImapFolder)));
+        $this->assertSame(['anyone' => ['p']], $imap->getACL(IMAP::toUTF7($newImapFolder)));
 
         // Delete the resource
         $this->assertTrue(IMAP::deleteResource($resource));
@@ -252,27 +250,28 @@
 
         $imap = $this->getImap();
         $expectedAcl = [
+            'anyone' => ['p'],
+            'jack@kolab.org' => str_split('lrs'),
             'john@kolab.org' => str_split('lrswipkxtecdn'),
-            'jack@kolab.org' => str_split('lrs')
         ];
 
         $acl = $imap->getACL(IMAP::toUTF7($imapFolder));
-        $this->assertTrue(is_array($acl) && isset($acl['john@kolab.org']));
-        $this->assertSame($expectedAcl['john@kolab.org'], $acl['john@kolab.org']);
-        $this->assertTrue(is_array($acl) && isset($acl['jack@kolab.org']));
-        $this->assertSame($expectedAcl['jack@kolab.org'], $acl['jack@kolab.org']);
+        ksort($acl);
+        $this->assertSame($expectedAcl, $acl);
 
         // Update shared folder (acl)
         $folder->setSetting('acl', json_encode(['jack@kolab.org, read-only']));
 
         $this->assertTrue(IMAP::updateSharedFolder($folder));
 
-        $expectedAcl = ['jack@kolab.org' => str_split('lrs')];
+        $expectedAcl = [
+            'anyone' => ['p'],
+            'jack@kolab.org' => str_split('lrs'),
+        ];
 
         $acl = $imap->getACL(IMAP::toUTF7($imapFolder));
-        $this->assertTrue(is_array($acl) && isset($acl['jack@kolab.org']));
-        $this->assertSame($expectedAcl['jack@kolab.org'], $acl['jack@kolab.org']);
-        $this->assertTrue(!isset($acl['john@kolab.org']));
+        ksort($acl);
+        $this->assertSame($expectedAcl, $acl);
 
         // Update the shared folder (rename)
         $folder->name = 'SharedFolder1 ©' . time();
@@ -284,8 +283,8 @@
         $this->assertTrue(IMAP::verifySharedFolder($newImapFolder));
 
         $acl = $imap->getACL(IMAP::toUTF7($newImapFolder));
-        $this->assertTrue(is_array($acl) && isset($acl['jack@kolab.org']));
-        $this->assertSame($expectedAcl['jack@kolab.org'], $acl['jack@kolab.org']);
+        ksort($acl);
+        $this->assertSame($expectedAcl, $acl);
 
         // Delete the shared folder
         $this->assertTrue(IMAP::deleteSharedFolder($folder));
diff --git a/src/tests/Feature/Backends/LDAPTest.php b/src/tests/Feature/Backends/LDAPTest.php
--- a/src/tests/Feature/Backends/LDAPTest.php
+++ b/src/tests/Feature/Backends/LDAPTest.php
@@ -247,7 +247,7 @@
             'kolabtargetfolder' => 'shared/Resources/Test1@kolab.org',
             'kolabinvitationpolicy' => null,
             'owner' => null,
-            'acl' => null,
+            'acl' => 'anyone, p',
         ];
 
         foreach ($expected as $attr => $value) {
@@ -267,7 +267,7 @@
         $expected['owner'] = 'uid=john@kolab.org,ou=People,ou=kolab.org,' . $root_dn;
         $expected['dn'] = 'cn=Te(\\3dść)1,ou=Resources,ou=kolab.org,' . $root_dn;
         $expected['cn'] = 'Te(=ść)1';
-        $expected['acl'] = 'john@kolab.org, full';
+        $expected['acl'] = ['john@kolab.org, full', 'anyone, p'];
 
         $ldap_resource = LDAP::getResource($resource->email);
 
@@ -281,7 +281,7 @@
 
         LDAP::updateResource($resource);
 
-        $expected['acl'] = null;
+        $expected['acl'] = 'anyone, p';
         $expected['kolabinvitationpolicy'] = null;
         $expected['owner'] = null;
 
@@ -330,7 +330,7 @@
             ],
             'kolabfoldertype' => 'event',
             'kolabtargetfolder' => 'shared/test-folder@kolab.org',
-            'acl' => null,
+            'acl' => 'anyone, p',
             'alias' => null,
         ];
 
@@ -349,7 +349,7 @@
         LDAP::updateSharedFolder($folder);
 
         $expected['kolabtargetfolder'] = 'shared/Te(=ść)1@kolab.org';
-        $expected['acl'] = ['john@kolab.org, read-write', 'anyone, read-only'];
+        $expected['acl'] = ['john@kolab.org, read-write', 'anyone, lrsp'];
         $expected['dn'] = 'cn=Te(\\3dść)1,ou=Shared Folders,ou=kolab.org,' . $root_dn;
         $expected['cn'] = 'Te(=ść)1';
         $expected['alias'] = $aliases;
diff --git a/src/tests/Unit/UtilsTest.php b/src/tests/Unit/UtilsTest.php
--- a/src/tests/Unit/UtilsTest.php
+++ b/src/tests/Unit/UtilsTest.php
@@ -58,6 +58,24 @@
         $this->assertSame('shared+shared/Test@test.tld', Utils::emailToLower('shared+shared/Test@Test.Tld'));
     }
 
+    /**
+     * Test for Utils::ensureAclPostPermission()
+     */
+    public function testEnsureAclPostPermission(): void
+    {
+        $acl = [];
+        $this->assertSame(['anyone, p'], Utils::ensureAclPostPermission($acl));
+
+        $acl = ['anyone, full'];
+        $this->assertSame(['anyone, full'], Utils::ensureAclPostPermission($acl));
+
+        $acl = ['anyone, read-only'];
+        $this->assertSame(['anyone, lrsp'], Utils::ensureAclPostPermission($acl));
+
+        $acl = ['anyone, read-write'];
+        $this->assertSame(['anyone, lrswitednp'], Utils::ensureAclPostPermission($acl));
+    }
+
     /**
      * Test for Utils::money()
      */