diff --git a/addressbook/inc/class.addressbook_ui.inc.php b/addressbook/inc/class.addressbook_ui.inc.php
index f0a4e03016..ef579fea64 100644
--- a/addressbook/inc/class.addressbook_ui.inc.php
+++ b/addressbook/inc/class.addressbook_ui.inc.php
@@ -162,14 +162,21 @@ class addressbook_ui extends addressbook_bo
 				{
 					$success = $failed = $action_msg = null;
 					if ($this->action($_content['nm']['action'],$_content['nm']['selected'],$_content['nm']['select_all'],
-						$success,$failed,$action_msg,'index',$msg,$_content['nm']['checkboxes']))
+						$success,$failed,$action_msg,'index',$msg,$_content['nm']['checkboxes'], $error_msg))
 					{
 						$msg .= lang('%1 contact(s) %2',$success,$action_msg);
 						Framework::message($msg);
 					}
 					elseif(is_null($msg))
 					{
-						$msg .= lang('%1 contact(s) %2, %3 failed because of insufficent rights !!!',$success,$action_msg,$failed);
+						if (empty($error_msg))
+						{
+							$msg .= lang('%1 contact(s) %2, %3 failed because of insufficent rights !!!', $success, $action_msg, $failed);
+						}
+						else
+						{
+							$msg .= lang('%1 contact(s) %2, %3 failed because of %4 !!!', $success, $action_msg, $failed, $error_msg);
+						}
 						Framework::message($msg,'error');
 					}
 					$msg = '';
@@ -1213,12 +1220,14 @@ class addressbook_ui extends addressbook_bo
 	 * @param int &$failed number of failed actions (not enought permissions)
 	 * @param string &$action_msg translated verb for the actions, to be used in a message like %1 contacts 'deleted'
 	 * @param string/array $session_name 'index' or array with session-data depending if we are in the main list or the popup
+	 * @param ?string& $error_msg on return optional error-message
 	 * @return boolean true if all actions succeded, false otherwise
 	 */
-	function action($action,$checked,$use_all,&$success,&$failed,&$action_msg,$session_name,&$msg, $checkboxes = NULL)
+	function action($action, $checked, $use_all, &$success, &$failed, &$action_msg, $session_name, &$msg, $checkboxes = NULL, &$error_msg=null)
 	{
 		//echo "<p>uicontacts::action('$action',".print_r($checked,true).','.(int)$use_all.",...)</p>\n";
 		$success = $failed = 0;
+		$error_msg = null;
 		if ($use_all || in_array($action,array('remove_from_list','delete_list','unshare')))
 		{
 			// get the whole selection
@@ -1509,8 +1518,10 @@ class addressbook_ui extends addressbook_bo
 							'shared_at' => new Api\DateTime('now'),
 							// only allow to share writable, if user has edit-rights!
 							'shared_writable' => (int)($checkboxes['writable'] && $this->check_perms(Acl::EDIT, $contact)),
+							'contact_id' => $id,
+							'contact' => $contact,
 						]];
-						if ($this->check_shared_with($new_shared_with))	// returns [] if OK
+						if ($this->check_shared_with($new_shared_with, $error_msg))	// returns [] if OK
 						{
 							$Ok = false;
 						}
@@ -2765,7 +2776,7 @@ class addressbook_ui extends addressbook_bo
 	/**
 	 * Check if user has right to share with / into given AB
 	 *
-	 * @param array $_data values for keys "shared_writable" and "shared_values"
+	 * @param array $_data values for keys "shared_writable", "shared_values" and "contact"
 	 * @return array of entries removed from $shared_with because current user is not allowed to share into
 	 */
 	public function ajax_check_shared(array $_data)
@@ -2787,11 +2798,12 @@ class addressbook_ui extends addressbook_bo
 				{
 					$shared[$value] = array_combine(['shared_id', 'shared_with', 'shared_by', 'shared_writable'], explode(':', $value));
 				}
+				$shared[$value]['contact'] = $_data['contact'];
 			}
-			if (($failed = $this->check_shared_with($shared)))
+			if (($failed = $this->check_shared_with($shared, $error)))
 			{
 				$response->data(array_keys($failed));
-				$response->message(lang('You are not allowed to share into the addressbook of %1',
+				$response->message($error ?: lang('You are not allowed to share into the addressbook of %1',
 					implode(', ', array_map(function ($data) {
 						return Api\Accounts::username($data['shared_with']);
 					}, $failed))), 'error');
diff --git a/addressbook/js/app.js b/addressbook/js/app.js
index e31c24b66c..1d193399ce 100644
--- a/addressbook/js/app.js
+++ b/addressbook/js/app.js
@@ -1229,6 +1229,7 @@ var AddressbookApp = /** @class */ (function (_super) {
         var value = (_a = shared) === null || _a === void 0 ? void 0 : _a.get_value();
         if (value) {
             this.egw.json('addressbook.addressbook_ui.ajax_check_shared', [{
+                    contact: this.et2.getInstanceManager().getValues(this.et2),
                     shared_values: value,
                     shared_writable: this.et2.getInputWidgetById('shared_writable').get_value()
                 }], function (_data) {
diff --git a/addressbook/js/app.ts b/addressbook/js/app.ts
index 95c3954b4d..18db4b1d86 100644
--- a/addressbook/js/app.ts
+++ b/addressbook/js/app.ts
@@ -1488,6 +1488,7 @@ class AddressbookApp extends EgwApp
 		if (value)
 		{
 			this.egw.json('addressbook.addressbook_ui.ajax_check_shared', [{
+				contact: this.et2.getInstanceManager().getValues(this.et2),	// for sharing policy
 				shared_values: value,
 				shared_writable: this.et2.getInputWidgetById('shared_writable').get_value()
 			}], _data => {
diff --git a/addressbook/lang/egw_de.lang b/addressbook/lang/egw_de.lang
index 53724700f1..db83580086 100644
--- a/addressbook/lang/egw_de.lang
+++ b/addressbook/lang/egw_de.lang
@@ -1,6 +1,7 @@
 %1 added	addressbook	de	%1 hinzugefügt
 %1 contact(s) %2	addressbook	de	%1 Kontakt(e) %2
-%1 contact(s) %2, %3 failed because of insufficent rights !!!	addressbook	de	%1 Kontakt(e) %2, %3 nicht wegen fehlender Rechte !!!
+%1 contact(s) %2, %3 failed because of %4 !!!	addressbook	de	%1 Kontakt(e) %2, %3 nicht da %4!
+%1 contact(s) %2, %3 failed because of insufficent rights !!!	addressbook	de	%1 Kontakt(e) %2, %3 nicht wegen fehlender Rechte!
 %1 contacts updated (%2 errors).	addressbook	de	%1 Kontakte aktualisiert (%2 Fehler).
 %1 fields in %2 other organisation member(s) changed	addressbook	de	%1 Felder in %2 Mitglied(ern) der Organisation geändert
 %1 key(s) added to public keyserver "%2".	addressbook	de	%1 Schlüssel wurden dem öffentlichen Schlüsselserver "%2" eingetragen.
@@ -433,7 +434,6 @@ replacements for inserting contacts into documents	addressbook	de	Platzhalter f
 required fields *	addressbook	de	unbedingt auszufüllende Felder *
 role	addressbook	de	Beruf
 room	addressbook	de	Raum
-schedule a video conference	addressbook	de	Videokonferenz planen
 search letter	addressbook	de	Suche nach Buchstaben
 select a portrait format jpeg photo. it will be resized to 60 pixel width.	addressbook	de	Wählen Sie ein hochformatiges jpeg Foto. Es wird 60 Pixel breit skaliert.
 select a source address to be used in geolocation routing system	addressbook	de	Legen Sie fest, wie der Startpunkt für die Routenplanung gesetzt wird.
diff --git a/addressbook/lang/egw_en.lang b/addressbook/lang/egw_en.lang
index 8b38d377ea..df1006285f 100644
--- a/addressbook/lang/egw_en.lang
+++ b/addressbook/lang/egw_en.lang
@@ -1,5 +1,6 @@
 %1 added	addressbook	en	%1 added
 %1 contact(s) %2	addressbook	en	%1 contact(s) %2
+%1 contact(s) %2, %3 failed because of %4 !!!	addressbook	en	%1 contact(s) %2, %3 failed because of %4 !!!
 %1 contact(s) %2, %3 failed because of insufficent rights !!!	addressbook	en	%1 contact(s) %2, %3 failed because of insufficient rights!
 %1 contacts updated (%2 errors).	addressbook	en	%1 contacts updated (%2 errors).
 %1 fields in %2 other organisation member(s) changed	addressbook	en	%1 fields in %2 other organization member(s) changed.
@@ -433,7 +434,6 @@ replacements for inserting contacts into documents	addressbook	en	Replacements f
 required fields *	addressbook	en	Required fields *
 role	addressbook	en	Occupation
 room	addressbook	en	Room
-schedule a video conference addressbook	en	Schedule a video conference
 search letter	addressbook	en	Search letter
 select a portrait format jpeg photo. it will be resized to 60 pixel width.	addressbook	en	Select a portrait format jpeg photo. It will be re-sized to 60 pixel width.
 select a source address to be used in geolocation routing system	addressbook	en	Select a source address to be used in GeoLocation routing system
diff --git a/admin/inc/class.admin_cmd.inc.php b/admin/inc/class.admin_cmd.inc.php
index b95b98c965..3e2456285b 100644
--- a/admin/inc/class.admin_cmd.inc.php
+++ b/admin/inc/class.admin_cmd.inc.php
@@ -606,6 +606,10 @@ abstract class admin_cmd
 					$class = 'EGroupware\\' . $class;
 					$label = $class::name();
 				}
+				else
+				{
+					unset($labels[$class]);
+				}
 			}
 
 			// sort them alphabetic
diff --git a/api/src/Contacts.php b/api/src/Contacts.php
index 906c354dc8..b67b09a4ac 100755
--- a/api/src/Contacts.php
+++ b/api/src/Contacts.php
@@ -1283,9 +1283,10 @@ class Contacts extends Contacts\Storage
 	 * Check if user has right to share with / into given AB
 	 *
 	 * @param array[]& $shared_with array of arrays with values for keys "shared_with", "shared_by", ...
+	 * @param ?string& $error on return error-message
 	 * @return array entries removed from $shared_with because current user is not allowed to share into (key is preserved)
 	 */
-	function check_shared_with(array &$shared_with=null)
+	function check_shared_with(array &$shared_with=null, &$error=null)
 	{
 		$removed = [];
 		foreach((array)$shared_with as $key => $shared)
@@ -1304,6 +1305,21 @@ class Contacts extends Contacts\Storage
 				unset($shared_with[$key]);
 			}
 		}
+		// allow apps to modifiy
+		$results = [];
+		foreach(Hooks::process([
+			'location' => 'check_shared_with',
+			'shared_with' => &$shared_with,
+			'removed' => &$removed,
+		], true) as $result)
+		{
+			if ($result)
+			{
+				$results = array_merge($results, $result);
+			}
+		}
+		if ($results) $error = implode("\n", $results);
+
 		return $removed;
 	}