suggestion implemented

--- ./lib/private/User/Manager.php	2023-02-03 17:18:44.729561986 +0530

+++ ./lib/private/User/Manager-new.php	2023-02-09 19:53:49.539733394 +0530

+++ ./lib/private/User/Manager-new.php	2023-02-09 21:41:35.339729765 +0530

@@ -705,6 +705,20 @@

 	 * @since 9.1.0

 	 */

+			$alt_domain_suffix ='@'  . $alt_domain;

+		}

+

+		if (stristr($email, $alt_domain_suffix) !== FALSE) {

+		if (!empty($alt_domain_suffix) && stristr($email, $alt_domain_suffix) !== FALSE) {

+			$uid = str_replace($alt_domain_suffix, '', $email);

+		}

+

+		if ($this->get($uid)) {

+			return([$this->get($uid)]);

+		if ($user = $this->get($uid)) {

+			return([$user]);

+		}

 		// looking for 'email' only (and not primary_mail) is intentional

 		$userIds = $this->config->getUsersForUserValueCaseInsensitive('settings', 'email', $email);