Backport virtuser file email2user fix (#9691)

* Merge pull request #9668 from idressos/virtuser_file-email2user-fix

Fix virtuser_file plugin email2user() function not accounting for backward slashes in username

Cherry-picked from 875e370 (parent mainline 1).

* Changelog entry for #9668

(cherry picked from commit a07d61a)

Author: pabzm

CHANGELOG.md

@@ -8,6 +8,7 @@
 - Fix current script state after initial scripts creation in managesieve_kolab_master mode
 - Fix rcube_imap::get_vendor() result (and PHP warning) on Zimbra server (#9650)
 - Fix regression causing inline SVG images to be missing in mail preview (#9644)
+- Fix plugin "virtuser_file" to handle backward slashes in username (#9668)
 
 ## Release 1.6.9
 

plugins/virtuser_file/virtuser_file.php

@@ -67,7 +67,9 @@ function email2user($p)
             $arr = preg_split('/\s+/', trim($r[$i]));
 
             if (count($arr) > 0) {
-                $p['user'] = trim($arr[count($arr)-1]);
+                // Replace '\@' with '@' to handle cases where internal usernames include an '@' character.
+                // Sometimes usernames with '@' are saved with a leading '\' to avoid conflicts.
+                $p['user'] = trim(str_replace('\@', '@', $arr[count($arr) - 1]));
                 break;
             }
         }