diff -urN ../z-push-2.6.4+0.orig/src/backend/imap/config.php ./src/backend/imap/config.php
--- ../z-push-2.6.4+0.orig/src/backend/imap/config.php	2021-06-25 11:55:30.000000000 +0300
+++ ./src/backend/imap/config.php	2021-12-23 21:52:36.817808000 +0200
@@ -158,6 +158,7 @@
 define('IMAP_FROM_LDAP_EMAIL', '#mail');
 define('IMAP_FROM_LDAP_FROM', '#givenname #sn <#mail>');
 define('IMAP_FROM_LDAP_FULLNAME', '#givenname #sn');
+define('IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR', false);
 
 
 
diff -urN ../z-push-2.6.4+0.orig/src/backend/imap/user_identity.php ./src/backend/imap/user_identity.php
--- ../z-push-2.6.4+0.orig/src/backend/imap/user_identity.php	2021-06-25 11:55:30.000000000 +0300
+++ ./src/backend/imap/user_identity.php	2023-06-18 22:02:56.007395000 +0300
@@ -158,15 +158,33 @@
                         }
                     }
                     else {
-                        ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getIdentityFromLdap() - No entry found in LDAP"));
+                        $message = sprintf("BackendIMAP->getIdentityFromLdap() - No entry found in LDAP for %s@%s", $username, ($domain ? '@' : '') . $domain);
+                        if (defined('IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR') and (IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR === true)) {
+                            ZLog::Write(LOGLEVEL_ERROR, $message);
+                            $ret_value = '';
+                        } else {
+                            ZLog::Write(LOGLEVEL_WARN, $message);
+                        }
                     }
                 }
                 else {
-                    ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getIdentityFromLdap() - Not authenticated in LDAP server"));
+                    $message = sprintf("BackendIMAP->getIdentityFromLdap() - Unable to bind to LDAP server %s", IMAP_FROM_LDAP_SERVER_URI);
+                    if (defined('IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR') and (IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR === true)) {
+                        ZLog::Write(LOGLEVEL_ERROR, $message);
+                        $ret_value = '';
+                    } else {
+                        ZLog::Write(LOGLEVEL_WARN, $message);
+                    }
                 }
             }
             else {
-                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getIdentityFromLdap() - Not connected to LDAP server"));
+                $message = sprintf("BackendIMAP->getIdentityFromLdap() - Unable to create LDAP object. May be incorrect IMAP_FROM_LDAP_SERVER_URI %s", IMAP_FROM_LDAP_SERVER_URI);
+                if (defined('IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR') and (IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR === true)) {
+                    ZLog::Write(LOGLEVEL_ERROR, $message);
+                    $ret_value = '';
+                } else {
+                    ZLog::Write(LOGLEVEL_WARN, $message);
+                }
             }
         }
         else {
@@ -175,10 +193,16 @@
     }
     catch(Exception $ex) {
         ZLog::Write(LOGLEVEL_WARN, sprintf("BackendIMAP->getIdentityFromLdap() - Error getting From value from LDAP server: %s", $ex));
+        if (defined('IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR') and (IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR === true)) $ret_value = '';
     }
 
     if ($ldap_conn != null) {
         ldap_close($ldap_conn);
+    }
+
+    if (defined('IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR') and (IMAP_FROM_LDAP_SERVICE_UNAVAILABLE_ON_ERROR === true) and ($ret_value == '')) {
+        throw new ServiceUnavailableException(sprintf("BackendIMAP->getIdentityFromLdap() - Error getting identity from LDAP server %s for %s%s",
+            IMAP_FROM_LDAP_SERVER_URI, $username, ($domain ? '@' : '') . $domain));
     }
 
     return $ret_value;