diff --git a/infolog/inc/class.infolog_groupdav.inc.php b/infolog/inc/class.infolog_groupdav.inc.php
index b7dbdb3a12..a7ed589cad 100644
--- a/infolog/inc/class.infolog_groupdav.inc.php
+++ b/infolog/inc/class.infolog_groupdav.inc.php
@@ -462,7 +462,12 @@ class infolog_groupdav extends groupdav_handler
 			$taskId = 0;
 			$retval = '201 Created';
 		}
-		if (!($infoId = $handler->importVTODO($vTodo, $taskId, false, $user, null, $id)))
+		if ($GLOBALS['egw_info']['user']['preferences']['groupdav']['infolog-cat-action'] &&
+			$GLOBALS['egw_info']['user']['preferences']['groupdav']['infolog-cat-action'] !== 'none')
+		{
+			$callback_data = array(array($this, 'cat_action'), $oldTask);
+		}
+		if (!($infoId = $handler->importVTODO($vTodo, $taskId, false, $user, null, $id, $callback_data)))
 		{
 			if ($this->debug) error_log(__METHOD__."(,$id) import_vtodo($options[content]) returned false");
 			return '403 Forbidden';
@@ -484,6 +489,71 @@ class infolog_groupdav extends groupdav_handler
 		return $retval;
 	}
 
+	/**
+	 * Callback for infolog_ical::importVTODO to implement infolog-cat-action
+	 *
+	 * @param array $task
+	 * @param array $oldTask=null
+	 * @return array modified task data
+	 */
+	public function cat_action(array $task, $oldTask=null)
+	{
+		$action = $GLOBALS['egw_info']['user']['preferences']['groupdav']['infolog-cat-action'];
+
+		//error_log(__METHOD__.'('.array2string($task).', '.array2string($oldTask).") action=$action");
+		if ($task['info_cat'] && ($new_cat = categories::id2name($task['info_cat'])) &&
+			strpos($new_cat, '@') !== false)
+		{
+			$new_user = $GLOBALS['egw']->accounts->name2id($new_cat, 'account_email');
+		}
+		$old_responsible = $task['info_responsible'];
+		// no action taken, if cat is not email of user
+		if ($new_user)
+		{
+			// make sure category is global, as otherwise it will not be transmitted to other users
+			if (!categories::is_global($task['info_cat']))
+			{
+				$cat_obj = new categories(categories::GLOBAL_ACCOUNT, 'infolog');
+				$cat = categories::read($task['info_cat']);
+				$cat['owner'] = categories::GLOBAL_ACCOUNT;
+				$cat['access'] = 'public';
+				$cat_obj->edit($cat);
+			}
+			// if replace, remove user of old category from responsible
+			if ($action == 'replace' && $oldTask && $oldTask['info_cat'] &&
+				($old_cat = categories::id2name($oldTask['info_cat'])) && strpos($old_cat, '@') !== false &&
+				($old_user = $GLOBALS['egw']->accounts->name2id($old_cat, 'account_email')) &&
+				($key = array_search($old_user, (array)$task['info_responsible'])) !== false)
+			{
+				unset($task['info_responsible'][$key]);
+			}
+			switch($action)
+			{
+				case 'set':
+					$task['info_responsible'] = array();
+					// fall through
+				case 'set-user':
+					foreach($task['info_responsible'] as $key => $account_id)
+					{
+						if ($GLOBALS['egw']->accounts->get_type($account_id) == 'u')
+						{
+							unset($task['info_responsible'][$key]);
+						}
+					}
+					// fall-through
+				case 'add':
+				case 'replace':
+					if (!in_array($new_user, (array)$task['info_responsible']))
+					{
+						$task['info_responsible'][] = $new_user;
+					}
+					break;
+			}
+		}
+		error_log(__METHOD__."() action=$action, new_cat=$new_cat --> new_user=$new_user, old_cat=$old_cat --> old_user=$old_user: responsible: ".array2string($old_responsible).' --> '.array2string($task['info_responsible']));
+		return $task;
+	}
+
 	/**
 	 * Handle delete request for a task / infolog entry
 	 *
@@ -647,6 +717,22 @@ class infolog_groupdav extends groupdav_handler
 			'xmlrpc' => True,
 			'admin'  => False,
 		);
+		$settings['infolog-cat-action'] = array(
+			'type'   => 'select',
+			'label'  => 'Action when category is an EMail address',
+			'name'   => 'infolog-cat-action',
+			'help'   => 'Allows to modify responsible users from devices not supporting them, by setting EMail address of a user as category.',
+			'values' => array(
+				'none' => lang('none'),
+				'add' => lang('add user to responsibles'),
+				'replace' => lang('add user to responsibles, removing evtl. previous category user'),
+				'set' => lang('set user as only responsible, removing all existing responsibles'),
+				'set-user' => lang('set user as only responsible user, but keeping groups'),
+			),
+			'default' => 'none',
+			'xmlrpc' => True,
+			'admin'  => False,
+		);
 		return $settings;
 	}
 }
diff --git a/infolog/inc/class.infolog_ical.inc.php b/infolog/inc/class.infolog_ical.inc.php
index 65a6fe2b07..186ef3fc05 100644
--- a/infolog/inc/class.infolog_ical.inc.php
+++ b/infolog/inc/class.infolog_ical.inc.php
@@ -513,9 +513,12 @@ class infolog_ical extends infolog_bo
 	 * @param string $charset=null The encoding charset for $text. Defaults to
      *                         utf-8 for new format, iso-8859-1 for old format.
      * @param string $caldav_name=null CalDAV URL name-part for new entries
+     * @param array $callback_data=null array with callback and further parameters, first param is task to save
+     * 	signature array callback($task, $param1, ...)
 	 * @return int|boolean integer info_id or false on error
 	 */
-	function importVTODO(&$_vcalData, $_taskID=-1, $merge=false, $user=null, $charset=null, $caldav_name=null)
+	function importVTODO(&$_vcalData, $_taskID=-1, $merge=false, $user=null, $charset=null, $caldav_name=null,
+		array $callback_data=null)
 	{
 
 		if ($this->tzid)
@@ -579,6 +582,12 @@ class infolog_ical extends infolog_bo
 			// merge in again all infolog fields not supported by iCal or not allowed to change
 			$taskData = array_merge($taskData, $old);
 		}
+		if ($callback_data)
+		{
+			$callback = array_shift($callback_data);
+			array_unshift($callback_data, $taskData);
+			$taskData = call_user_func_array($callback, $callback_data);
+		}
 		return $this->write($taskData, true, true, false, false, false, 'ical');
 	}
 
diff --git a/phpgwapi/lang/egw_de.lang b/phpgwapi/lang/egw_de.lang
index 00dffb2620..2b9667cb6d 100644
--- a/phpgwapi/lang/egw_de.lang
+++ b/phpgwapi/lang/egw_de.lang
@@ -33,6 +33,7 @@ account is expired	common	de	Benutzerkennung ist abgelaufen
 accounts	common	de	Benutzerkonten
 acl	common	de	ACL
 action	common	de	Aktion
+action when category is an email address	groupdav	de	Aktion wenn Kategorie eine EMail Adresse ist
 actions	common	de	Befehle
 active	common	de	Aktiv
 add	common	de	Hinzufügen
@@ -40,6 +41,8 @@ add %1 category for	common	de	%1 Kategorie hinzufügen für
 add category	common	de	Kategorie hinzufügen
 add shortcut	common	de	Abkürzung hinzufügen
 add sub	common	de	Untergeordnete hinzufügen
+add user to responsibles	groupdav	de	füge Benutzer zu Verantwortlichen hinzu
+add user to responsibles, removing evtl. previous category user	groupdav	de	füge Benutzer zu Verantwortlichen hinzu, entferne Benutzer der vorherigen Kategorie
 addressbook	common	de	Adressbuch
 addressbooks to sync in addition to personal addressbook	groupdav	de	Adressbücher die zusätzlich zum persönlichen synchronisiert werden sollen
 admin	common	de	Admin
@@ -52,6 +55,7 @@ all addressbooks	groupdav	de	Alle Adressbücher
 all fields	common	de	alle Felder
 all in one	groupdav	de	Gemeinsam in einem
 all languages	common	de	Alle Sprachen
+allows to modify responsible users from devices not supporting them, by setting email address of a user as category.	groupdav	de	Erlaubt verantwortliche Benutzer durch setzen einer EMail Adresse als Kategorie zu ändern, von Geräten die keine verantwortlichen Benutzer unterstützen.
 alphabet	common	de	a,ä,b,c,d,e,f,g,h,i,j,k,l,m,n,o,ö,p,q,r,s,t,u,ü,v,w,x,y,z
 alternate style-sheet:	common	de	Alternatives Style-sheet
 american samoa	common	de	AMERICANISCH SAMOA
@@ -646,6 +650,8 @@ server answered. processing response...	common	de	Server antwortet. Bearbeite An
 server contacted. waiting for response...	common	de	Server kontaktiert. Warte auf Antwort...
 server name	common	de	Server Name
 session has been killed	common	de	Session wurde beendet
+set user as only responsible user, but keeping groups	groupdav	de	setze Benutzer als einzigen verantwortlichen Benutzer, Gruppen werden nicht geändert
+set user as only responsible, removing all existing responsibles	groupdav	de	setze Benutzer als alleinigen Verantwortlichen, entferne alle bestehenden Verantwortlichen
 setup	common	de	Setup
 setup main menu	common	de	Setup Hauptmenü
 seychelles	common	de	SEYCHELLEN
diff --git a/phpgwapi/lang/egw_en.lang b/phpgwapi/lang/egw_en.lang
index 5f67eb0ec0..5b1d1ce6a7 100644
--- a/phpgwapi/lang/egw_en.lang
+++ b/phpgwapi/lang/egw_en.lang
@@ -33,6 +33,7 @@ account is expired	common	en	Account is expired.
 accounts	common	en	Accounts
 acl	common	en	ACL
 action	common	en	Action
+action when category is an email address	groupdav	en	Action when category is an EMail address
 actions	common	en	Actions
 active	common	en	Active
 add	common	en	Add
@@ -40,6 +41,8 @@ add %1 category for	common	en	Add %1 category for
 add category	common	en	Add category
 add shortcut	common	en	Add shortcut
 add sub	common	en	Add sub
+add user to responsibles	groupdav	en	add user to responsibles
+add user to responsibles, removing evtl. previous category user	groupdav	en	add user to responsibles, removing evtl. previous category user
 addressbook	common	en	Address Book
 addressbooks to sync in addition to personal addressbook	groupdav	en	Addressbooks to sync in addition to personal addressbook
 admin	common	en	Admin
@@ -52,6 +55,7 @@ all addressbooks	groupdav	en	All addressbooks
 all fields	common	en	All fields
 all in one	groupdav	en	All in one
 all languages	common	en	All languages
+allows to modify responsible users from devices not supporting them, by setting email address of a user as category.	groupdav	en	Allows to modify responsible users from devices not supporting them, by setting EMail address of a user as category.
 alphabet	common	en	a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z
 alternate style-sheet:	common	en	Alternate style sheet:
 american samoa	common	en	AMERICAN SAMOA
@@ -647,6 +651,8 @@ server answered. processing response...	common	en	Server answered. Processing re
 server contacted. waiting for response...	common	en	Server contacted. Waiting for response...
 server name	common	en	Server name
 session has been killed	common	en	Session has been killed.
+set user as only responsible user, but keeping groups	groupdav	en	set user as only responsible user, but keeping groups
+set user as only responsible, removing all existing responsibles	groupdav	en	set user as only responsible, removing all existing responsibles
 setup	common	en	Setup
 setup main menu	common	en	Setup main menu
 seychelles	common	en	SEYCHELLES