diff --git a/api/src/Mail/Credentials.php b/api/src/Mail/Credentials.php
index bf8fc85c3b..c4f383860e 100644
--- a/api/src/Mail/Credentials.php
+++ b/api/src/Mail/Credentials.php
@@ -298,6 +298,13 @@ class Credentials
 	 */
 	public static function from_session(array $data, $set_identity=true)
 	{
+		// if the username contains non-ascii chars, try email address, as Dovecot does NOT deal with non-ascii usernames
+		if ($data['acc_imap_type'] === Api\Mail\Imap\Dovecot::class &&
+			in_array($data['acc_imap_logintype'], ['standard', 'vmailmgr']) &&
+			preg_match('/[^\x20-\x7e]/', $GLOBALS['egw_info']['user']['account_lid']))
+		{
+			$data['acc_imap_logintype'] = 'email';
+		}
 		switch($data['acc_imap_logintype'])
 		{
 			case 'standard':