diff --git a/apps/user_ldap/lib/Group_LDAP.php b/apps/user_ldap/lib/Group_LDAP.php
index 6f6e7362e9..199865e762 100644
--- a/apps/user_ldap/lib/Group_LDAP.php
+++ b/apps/user_ldap/lib/Group_LDAP.php
@@ -20,6 +20,7 @@
  * @author Roeland Jago Douma <roeland@famdouma.nl>
  * @author Roland Tapken <roland@bitarbeiter.net>
  * @author Thomas Müller <thomas.mueller@tmit.eu>
+ * @author Tobias Perschon <tobias@perschon.at>
  * @author Victor Dubiniuk <dubiniuk@owncloud.com>
  * @author Vincent Petry <pvince81@owncloud.com>
  * @author Vinicius Cubas Brand <vinicius@eita.org.br>
@@ -66,6 +67,11 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 	/** @var ILogger */
 	protected $logger;
 
+	/**
+	 * @var string $ldapGroupMemberAssocAttr contains the LDAP setting (in lower case) with the same name
+	 */
+	protected $ldapGroupMemberAssocAttr;
+
 	public function __construct(Access $access, GroupPluginManager $groupPluginManager) {
 		parent::__construct($access);
 		$filter = $this->access->connection->ldapGroupFilter;
@@ -79,6 +85,7 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		$this->cachedNestedGroups = new CappedMemoryCache();
 		$this->groupPluginManager = $groupPluginManager;
 		$this->logger = OC::$server->getLogger();
+		$this->ldapGroupMemberAssocAttr = strtolower($gAssoc);
 	}
 
 	/**
@@ -136,31 +143,38 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		}
 
 		//extra work if we don't get back user DNs
-		if (strtolower($this->access->connection->ldapGroupMemberAssocAttr) === 'memberuid') {
-			$requestAttributes = $this->access->userManager->getAttributes(true);
-			$dns = [];
-			$filterParts = [];
-			$bytes = 0;
-			foreach ($members as $mid) {
-				$filter = str_replace('%uid', $mid, $this->access->connection->ldapLoginFilter);
-				$filterParts[] = $filter;
-				$bytes += strlen($filter);
-				if ($bytes >= 9000000) {
-					// AD has a default input buffer of 10 MB, we do not want
-					// to take even the chance to exceed it
+		switch ($this->ldapGroupMemberAssocAttr) {
+			case 'memberuid':
+			case 'zimbramailforwardingaddress':
+				$requestAttributes = $this->access->userManager->getAttributes(true);
+				$dns = [];
+				$filterParts = [];
+				$bytes = 0;
+				foreach ($members as $mid) {
+					if ($this->ldapGroupMemberAssocAttr === 'zimbramailforwardingaddress') {
+						$parts = explode('@', $mid); //making sure we get only the uid
+						$mid = $parts[0];
+					}
+					$filter = str_replace('%uid', $mid, $this->access->connection->ldapLoginFilter);
+					$filterParts[] = $filter;
+					$bytes += strlen($filter);
+					if ($bytes >= 9000000) {
+						// AD has a default input buffer of 10 MB, we do not want
+						// to take even the chance to exceed it
+						$filter = $this->access->combineFilterWithOr($filterParts);
+						$users = $this->access->fetchListOfUsers($filter, $requestAttributes, count($filterParts));
+						$bytes = 0;
+						$filterParts = [];
+						$dns = array_merge($dns, $users);
+					}
+				}
+				if (count($filterParts) > 0) {
 					$filter = $this->access->combineFilterWithOr($filterParts);
-					$bytes = 0;
-					$filterParts = [];
 					$users = $this->access->fetchListOfUsers($filter, $requestAttributes, count($filterParts));
 					$dns = array_merge($dns, $users);
 				}
-			}
-			if (count($filterParts) > 0) {
-				$filter = $this->access->combineFilterWithOr($filterParts);
-				$users = $this->access->fetchListOfUsers($filter, $requestAttributes, count($filterParts));
-				$dns = array_merge($dns, $users);
-			}
-			$members = $dns;
+				$members = $dns;
+				break;
 		}
 
 		$isInGroup = in_array($userDN, $members);
@@ -673,8 +687,8 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		// memberof doesn't support memberuid, so skip it here.
 		if ((int)$this->access->connection->hasMemberOfFilterSupport === 1
 			&& (int)$this->access->connection->useMemberOfToDetectMembership === 1
-			&& strtolower($this->access->connection->ldapGroupMemberAssocAttr) !== 'memberuid'
-		) {
+			&& $this->ldapGroupMemberAssocAttr !== 'memberuid'
+			&& $this->ldapGroupMemberAssocAttr !== 'zimbramailforwardingaddress') {
 			$groupDNs = $this->_getGroupDNsFromMemberOf($userDN);
 			if (is_array($groupDNs)) {
 				foreach ($groupDNs as $dn) {
@@ -698,27 +712,33 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		}
 
 		//uniqueMember takes DN, memberuid the uid, so we need to distinguish
-		if ((strtolower($this->access->connection->ldapGroupMemberAssocAttr) === 'uniquemember')
-			|| (strtolower($this->access->connection->ldapGroupMemberAssocAttr) === 'member')
-		) {
-			$uid = $userDN;
-		} elseif (strtolower($this->access->connection->ldapGroupMemberAssocAttr) === 'memberuid') {
-			$result = $this->access->readAttribute($userDN, 'uid');
-			if ($result === false) {
-				$this->logger->debug('No uid attribute found for DN {dn} on {host}',
-					[
-						'app' => 'user_ldap',
-						'dn' => $userDN,
-						'host' => $this->access->connection->ldapHost,
-					]
-				);
-				$uid = false;
-			} else {
-				$uid = $result[0];
-			}
-		} else {
-			// just in case
-			$uid = $userDN;
+		switch ($this->ldapGroupMemberAssocAttr) {
+			case 'uniquemember':
+			case 'member':
+				$uid = $userDN;
+				break;
+
+			case 'memberuid':
+			case 'zimbramailforwardingaddress':
+				$result = $this->access->readAttribute($userDN, 'uid');
+				if ($result === false) {
+					$this->logger->debug('No uid attribute found for DN {dn} on {host}',
+						[
+							'app' => 'user_ldap',
+							'dn' => $userDN,
+							'host' => $this->access->connection->ldapHost,
+						]
+					);
+					$uid = false;
+				} else {
+					$uid = $result[0];
+				}
+				break;
+
+			default:
+				// just in case
+				$uid = $userDN;
+				break;
 		}
 
 		if ($uid !== false) {
@@ -759,6 +779,12 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		$allGroups = [];
 		$seen[$dn] = true;
 		$filter = $this->access->connection->ldapGroupMemberAssocAttr . '=' . $dn;
+
+		if ($this->ldapGroupMemberAssocAttr === 'zimbramailforwardingaddress') {
+			//in this case the member entries are email addresses
+			$filter .= '@*';
+		}
+
 		$groups = $this->access->fetchListOfGroups($filter,
 			[strtolower($this->access->connection->ldapGroupMemberAssocAttr), $this->access->connection->ldapGroupDisplayName, 'dn']);
 		if (is_array($groups)) {
@@ -768,6 +794,11 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 				}
 				return $this->getGroupsByMember($dn, $seen);
 			};
+
+			if (empty($dn)) {
+				$dn = "";
+			}
+
 			$allGroups = $this->walkNestedGroups($dn, $fetcher, $groups);
 		}
 		$visibleGroups = $this->filterValidGroups($allGroups);
@@ -828,50 +859,57 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		}
 
 		$groupUsers = [];
-		$isMemberUid = (strtolower($this->access->connection->ldapGroupMemberAssocAttr) === 'memberuid');
 		$attrs = $this->access->userManager->getAttributes(true);
 		foreach ($members as $member) {
-			if ($isMemberUid) {
-				//we got uids, need to get their DNs to 'translate' them to user names
-				$filter = $this->access->combineFilterWithAnd([
-					str_replace('%uid', trim($member), $this->access->connection->ldapLoginFilter),
-					$this->access->combineFilterWithAnd([
-						$this->access->getFilterPartForUserSearch($search),
-						$this->access->connection->ldapUserFilter
-					])
-				]);
-				$ldap_users = $this->access->fetchListOfUsers($filter, $attrs, 1);
-				if (count($ldap_users) < 1) {
-					continue;
-				}
-				$groupUsers[] = $this->access->dn2username($ldap_users[0]['dn'][0]);
-			} else {
-				//we got DNs, check if we need to filter by search or we can give back all of them
-				$uid = $this->access->dn2username($member);
-				if (!$uid) {
-					continue;
-				}
-
-				$cacheKey = 'userExistsOnLDAP' . $uid;
-				$userExists = $this->access->connection->getFromCache($cacheKey);
-				if ($userExists === false) {
-					continue;
-				}
-				if ($userExists === null || $search !== '') {
-					if (!$this->access->readAttribute($member,
-						$this->access->connection->ldapUserDisplayName,
+			switch ($this->ldapGroupMemberAssocAttr) {
+				case 'zimbramailforwardingaddress':
+					//we get email addresses and need to convert them to uids
+					$parts = explode('@', $member);
+					$member = $parts[0];
+					//no break needed because we just needed to remove the email part and now we have uids
+				case 'memberuid':
+					//we got uids, need to get their DNs to 'translate' them to user names
+					$filter = $this->access->combineFilterWithAnd([
+						str_replace('%uid', trim($member), $this->access->connection->ldapLoginFilter),
 						$this->access->combineFilterWithAnd([
 							$this->access->getFilterPartForUserSearch($search),
 							$this->access->connection->ldapUserFilter
-						]))) {
-						if ($search === '') {
-							$this->access->connection->writeToCache($cacheKey, false);
-						}
+						])
+					]);
+					$ldap_users = $this->access->fetchListOfUsers($filter, $attrs, 1);
+					if (count($ldap_users) < 1) {
 						continue;
 					}
-					$this->access->connection->writeToCache($cacheKey, true);
-				}
-				$groupUsers[] = $uid;
+					$groupUsers[] = $this->access->dn2username($ldap_users[0]['dn'][0]);
+					break;
+				default:
+					//we got DNs, check if we need to filter by search or we can give back all of them
+					$uid = $this->access->dn2username($member);
+					if (!$uid) {
+						continue;
+					}
+
+					$cacheKey = 'userExistsOnLDAP' . $uid;
+					$userExists = $this->access->connection->getFromCache($cacheKey);
+					if ($userExists === false) {
+						continue;
+					}
+					if ($userExists === null || $search !== '') {
+						if (!$this->access->readAttribute($member,
+							$this->access->connection->ldapUserDisplayName,
+							$this->access->combineFilterWithAnd([
+								$this->access->getFilterPartForUserSearch($search),
+								$this->access->connection->ldapUserFilter
+							]))) {
+							if ($search === '') {
+								$this->access->connection->writeToCache($cacheKey, false);
+							}
+							continue;
+						}
+						$this->access->connection->writeToCache($cacheKey, true);
+					}
+					$groupUsers[] = $uid;
+					break;
 			}
 		}
 
@@ -930,8 +968,8 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		}
 		$search = $this->access->escapeFilterPart($search, true);
 		$isMemberUid =
-			(strtolower($this->access->connection->ldapGroupMemberAssocAttr)
-				=== 'memberuid');
+			($this->ldapGroupMemberAssocAttr === 'memberuid' ||
+				$this->ldapGroupMemberAssocAttr === 'zimbramailforwardingaddress');
 
 		//we need to apply the search filter
 		//alternatives that need to be checked:
@@ -944,6 +982,11 @@ class Group_LDAP extends BackendUtility implements GroupInterface, IGroupLDAP, I
 		$groupUsers = [];
 		foreach ($members as $member) {
 			if ($isMemberUid) {
+				if ($this->ldapGroupMemberAssocAttr === 'zimbramailforwardingaddress') {
+					//we get email addresses and need to convert them to uids
+					$parts = explode('@', $member);
+					$member = $parts[0];
+				}
 				//we got uids, need to get their DNs to 'translate' them to user names
 				$filter = $this->access->combineFilterWithAnd([
 					str_replace('%uid', $member, $this->access->connection->ldapLoginFilter),
diff --git a/apps/user_ldap/lib/Wizard.php b/apps/user_ldap/lib/Wizard.php
index 73032bfd7f..32ad19efa5 100644
--- a/apps/user_ldap/lib/Wizard.php
+++ b/apps/user_ldap/lib/Wizard.php
@@ -794,7 +794,7 @@ class Wizard extends LDAPUtility {
 	 * @throws \Exception
 	 */
 	private function detectGroupMemberAssoc() {
-		$possibleAttrs = ['uniqueMember', 'memberUid', 'member', 'gidNumber'];
+		$possibleAttrs = ['uniqueMember', 'memberUid', 'member', 'gidNumber', 'zimbraMailForwardingAddress'];
 		$filter = $this->configuration->ldapGroupFilter;
 		if (empty($filter)) {
 			return false;
diff --git a/apps/user_ldap/templates/settings.php b/apps/user_ldap/templates/settings.php
index 6b0221f093..32dfdd12ab 100644
--- a/apps/user_ldap/templates/settings.php
+++ b/apps/user_ldap/templates/settings.php
@@ -103,7 +103,10 @@ style('user_ldap', 'settings');
 		p(' selected');
 	} ?>>member (AD)</option><option value="gidNumber"<?php if (isset($_['ldap_group_member_assoc_attribute']) && ($_['ldap_group_member_assoc_attribute'] === 'gidNumber')) {
 		p(' selected');
-	} ?>>gidNumber</option></select></p>				<p><label for="ldap_dynamic_group_member_url"><?php p($l->t('Dynamic Group Member URL'));?></label><input type="text" id="ldap_dynamic_group_member_url" name="ldap_dynamic_group_member_url" title="<?php p($l->t('The LDAP attribute that on group objects contains an LDAP search URL that determines what objects belong to the group. (An empty setting disables dynamic group membership functionality.)'));?>" data-default="<?php p($_['ldap_dynamic_group_member_url_default']); ?>" /></p>
+	} ?>>gidNumber</option><option value="zimbraMailForwardingAddress"<?php if (isset($_['ldap_group_member_assoc_attribute']) && ($_['ldap_group_member_assoc_attribute'] === 'zimbraMailForwardingAddress')) {
+		p(' selected');
+	} ?>>zimbraMailForwardingAddress</option></select></p>
+				<p><label for="ldap_dynamic_group_member_url"><?php p($l->t('Dynamic Group Member URL'));?></label><input type="text" id="ldap_dynamic_group_member_url" name="ldap_dynamic_group_member_url" title="<?php p($l->t('The LDAP attribute that on group objects contains an LDAP search URL that determines what objects belong to the group. (An empty setting disables dynamic group membership functionality.)'));?>" data-default="<?php p($_['ldap_dynamic_group_member_url_default']); ?>" /></p>
 				<p><label for="ldap_nested_groups"><?php p($l->t('Nested Groups'));?></label><input type="checkbox" id="ldap_nested_groups" name="ldap_nested_groups" value="1" data-default="<?php p($_['ldap_nested_groups_default']); ?>"  title="<?php p($l->t('When switched on, groups that contain groups are supported. (Only works if the group member attribute contains DNs.)'));?>" /></p>
 				<p><label for="ldap_paging_size"><?php p($l->t('Paging chunksize'));?></label><input type="number" id="ldap_paging_size" name="ldap_paging_size" title="<?php p($l->t('Chunksize used for paged LDAP searches that may return bulky results like user or group enumeration. (Setting it 0 disables paged LDAP searches in those situations.)'));?>" data-default="<?php p($_['ldap_paging_size_default']); ?>" /></p>
 				<p><label for="ldap_turn_on_pwd_change"><?php p($l->t('Enable LDAP password changes per user'));?></label><span class="inlinetable"><span class="tablerow left"><input type="checkbox" id="ldap_turn_on_pwd_change" name="ldap_turn_on_pwd_change" value="1" data-default="<?php p($_['ldap_turn_on_pwd_change_default']); ?>" title="<?php p($l->t('Allow LDAP users to change their password and allow Super Administrators and Group Administrators to change the password of their LDAP users. Only works when access control policies are configured accordingly on the LDAP server. As passwords are sent in plaintext to the LDAP server, transport encryption must be used and password hashing should be configured on the LDAP server.'));?>" /><span class="tablecell"><?php p($l->t('(New password is sent as plain text to LDAP)'));?></span></span>