diff -urN ../z-push-2.6.2+0.orig/src/backend/searchldap/config.php ./src/backend/searchldap/config.php
--- ../z-push-2.6.2+0.orig/src/backend/searchldap/config.php	2021-02-04 03:38:38.000000000 +0200
+++ ./src/backend/searchldap/config.php	2022-01-30 13:35:50.442340000 +0200
@@ -26,6 +26,18 @@
 
 // LDAP server uri
 define("LDAP_SERVER_URI", "ldap://127.0.0.1:389/");
+//define("LDAP_START_TLS", false);
+
+//define("LDAP_SERVER_URI", "ldaps://127.0.0.1:636/");
+//define("LDAP_DISABLE_REFERRALS", true);
+
+// Multi servers settings
+//define("LDAP_SERVER_CONF", array(
+//    "ldap://127.0.0.1:389/",
+//    array("LDAP_SERVER_URI" => "ldap://192.168.1.1:3268/", "LDAP_START_TLS" => true),
+//    array("LDAP_SERVER_URI" => "ldaps://127.0.0.1:636/", "LDAP_START_TLS" => false, "LDAP_DISABLE_REFERRALS" => true)
+//));
+//define("LDAP_BIND_TIMEOUT", 10);
 
 // Set USER and PASSWORD if not using anonymous bind
 define("ANONYMOUS_BIND", true);
diff -urN ../z-push-2.6.2+0.orig/src/backend/searchldap/searchldap.php ./src/backend/searchldap/searchldap.php
--- ../z-push-2.6.2+0.orig/src/backend/searchldap/searchldap.php	2021-02-04 03:38:38.000000000 +0200
+++ ./src/backend/searchldap/searchldap.php	2023-09-26 20:11:27.701668000 +0300
@@ -44,34 +44,145 @@
             throw new StatusException("BackendSearchLDAP(): php-ldap is not installed. Search aborted.", SYNC_SEARCHSTATUS_STORE_SERVERERROR, null, LOGLEVEL_FATAL);
         }
 
-        // Connect
-        if (defined('LDAP_SERVER_URI')) {
-            $this->connection = @ldap_connect(LDAP_SERVER_URI);
-            @ldap_set_option($this->connection, LDAP_OPT_PROTOCOL_VERSION, 3);
+        if (defined('LDAP_SERVER_CONF') and (is_array(LDAP_SERVER_CONF))) {
+            $ldap_server_conf = LDAP_SERVER_CONF;
         }
         else {
-            $this->connection = false;
-            throw new StatusException("BackendSearchLDAP(): No LDAP server URI defined! Search aborted.", SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+            $ldap_server_conf_item = array();
+            if (defined('LDAP_SERVER_URI')) {
+                $ldap_server_conf_item['LDAP_SERVER_URI'] = LDAP_SERVER_URI;
+            } else {
+                $this->connection = false;
+                throw new StatusException("BackendSearchLDAP(): No LDAP server URI defined. Search aborted.", SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+            }
+            if (defined('LDAP_DISABLE_REFERRALS') and (constant('LDAP_DISABLE_REFERRALS') === true)) {
+                $ldap_server_conf_item['LDAP_DISABLE_REFERRALS'] = true;
+            }
+            if (defined('LDAP_START_TLS') and (constant('LDAP_START_TLS') === true)) {
+                $ldap_server_conf_item['LDAP_START_TLS'] = true;
+            }
+            $ldap_server_conf = array($ldap_server_conf_item);
         }
 
-        // Authenticate
-        if (constant('ANONYMOUS_BIND') === true) {
-            if(! @ldap_bind($this->connection)) {
+        ZLog::Write(LOGLEVEL_DEBUG, "\$ldap_server_conf: " . print_r($ldap_server_conf, true));
+
+        while ($ldap_server_conf_item = array_shift($ldap_server_conf)) {
+            if (!is_array($ldap_server_conf_item)) {
+                $ldap_server_conf_item = array('LDAP_SERVER_URI' => $ldap_server_conf_item);
+            }
+            if (!isset($ldap_server_conf_item['ANONYMOUS_BIND'])) {
+                $ldap_server_conf_item['ANONYMOUS_BIND'] = (defined('ANONYMOUS_BIND') and (constant('ANONYMOUS_BIND') === true) ? true : false);
+            }
+            if (!isset($ldap_server_conf_item['LDAP_BIND_USER']) and defined('LDAP_BIND_USER')) {
+                $ldap_server_conf_item['LDAP_BIND_USER'] = LDAP_BIND_USER;
+            }
+            if (!isset($ldap_server_conf_item['LDAP_BIND_PASSWORD']) and defined('LDAP_BIND_PASSWORD')) {
+                $ldap_server_conf_item['LDAP_BIND_PASSWORD'] = LDAP_BIND_PASSWORD;
+            }
+            if (!isset($ldap_server_conf_item['LDAP_BIND_TIMEOUT']) and defined('LDAP_BIND_TIMEOUT')) {
+                $ldap_server_conf_item['LDAP_BIND_TIMEOUT'] = LDAP_BIND_TIMEOUT;
+            }
+
+            ZLog::Write(LOGLEVEL_DEBUG, "\$ldap_server_conf_item: " . print_r($ldap_server_conf_item, true));
+
+            // Connect
+            if (empty($ldap_server_conf_item['LDAP_SERVER_URI'])) {
                 $this->connection = false;
-                throw new StatusException("BackendSearchLDAP(): Could not bind anonymously to server! Search aborted.", SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+                if (count($ldap_server_conf) > 0) {
+                    ZLog::Write(LOGLEVEL_ERROR, sprintf("BackendSearchLDAP(): No LDAP server URI defined. Try next server."));
+                    continue;
+                }
+                else {
+                    throw new StatusException("BackendSearchLDAP(): No LDAP server URI defined. Search aborted.", SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+                }
             }
-        }
-        else if (constant('LDAP_BIND_USER') != "") {
-            if(! @ldap_bind($this->connection, LDAP_BIND_USER, LDAP_BIND_PASSWORD)) {
+            else {
+                ZLog::Write(LOGLEVEL_INFO, sprintf("BackendSearchLDAP(): Try to connect to %s", $ldap_server_conf_item['LDAP_SERVER_URI']));
+                $this->connection = @ldap_connect($ldap_server_conf_item['LDAP_SERVER_URI']);
+                if (!is_resource($this->connection)) {
+                    if (count($ldap_server_conf) > 0) {
+                        ZLog::Write(LOGLEVEL_ERROR, sprintf("BackendSearchLDAP(): Incorrect LDAP_SERVER_URI '%s'. Try next server.", $ldap_server_conf_item['LDAP_SERVER_URI']));
+                        continue;
+                    }
+                    else {
+                        throw new StatusException(sprintf("BackendSearchLDAP(): Incorrect LDAP_SERVER_URI '%s'. Search aborted.", $ldap_server_conf_item['LDAP_SERVER_URI']), SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+                    }
+                }
+                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendSearchLDAP(): Set LDAP_OPT_PROTOCOL_VERSION to 3"));
+                @ldap_set_option($this->connection, LDAP_OPT_PROTOCOL_VERSION, 3);
+            }
+
+            if (!empty($ldap_server_conf_item['LDAP_DISABLE_REFERRALS']) and ($ldap_server_conf_item['LDAP_DISABLE_REFERRALS'] === true)) {
+                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendSearchLDAP(): Set LDAP_OPT_REFERRALS to 0"));
+                @ldap_set_option($this->connection, LDAP_OPT_REFERRALS, 0);
+            }
+
+            if (!empty($ldap_server_conf_item['LDAP_BIND_TIMEOUT'])) {
+                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendSearchLDAP(): Set LDAP_OPT_NETWORK_TIMEOUT to %d", $ldap_server_conf_item['LDAP_BIND_TIMEOUT']));
+                @ldap_set_option($this->connection, LDAP_OPT_NETWORK_TIMEOUT, $ldap_server_conf_item['LDAP_BIND_TIMEOUT']);
+            }
+
+            if (!empty($ldap_server_conf_item['LDAP_START_TLS']) and ($ldap_server_conf_item['LDAP_START_TLS'] === true)) {
+                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendSearchLDAP(): Try to start TLS"));
+                if (! @ldap_start_tls($this->connection)) {
+                    $ldap_errno = ldap_errno($this->connection);
+                    $ldap_error = ldap_error($this->connection);
+                    $this->connection = false;
+                    if (count($ldap_server_conf) > 0) {
+                        ZLog::Write(LOGLEVEL_ERROR, sprintf("BackendSearchLDAP(): Could not start TLS session with server (error %d: %s). Try next server.", $ldap_errno, $ldap_error));
+                        continue;
+                    }
+                    else {
+                        throw new StatusException(sprintf("BackendSearchLDAP(): Could not start TLS session with server (error %d: %s). Search aborted.", $ldap_errno, $ldap_error), SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+                    }
+                }
+            }
+
+            // Authenticate
+            if (isset($ldap_server_conf_item['ANONYMOUS_BIND']) and ($ldap_server_conf_item['ANONYMOUS_BIND'] === true)) {
+                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendSearchLDAP(): Try to bind anonymously"));
+                if(! @ldap_bind($this->connection)) {
+                    $ldap_errno = ldap_errno($this->connection);
+                    $ldap_error = ldap_error($this->connection);
+                    $this->connection = false;
+                    if (count($ldap_server_conf) > 0) {
+                        ZLog::Write(LOGLEVEL_ERROR, sprintf("BackendSearchLDAP(): Could not bind anonymously to server (error %d: %s). Try next server.", $ldap_errno, $ldap_error));
+                        continue;
+                    }
+                    else {
+                        throw new StatusException(sprintf("BackendSearchLDAP(): Could not bind anonymously to server (error %d: %s). Search aborted.", $ldap_errno, $ldap_error), SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+                    }
+                }
+                return;
+            }
+            else if (!empty($ldap_server_conf_item['LDAP_BIND_USER']) and !empty($ldap_server_conf_item['LDAP_BIND_PASSWORD'])) {
+                ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendSearchLDAP(): Try to bind as user '%s'", $ldap_server_conf_item['LDAP_BIND_USER']));
+                if(! @ldap_bind($this->connection, $ldap_server_conf_item['LDAP_BIND_USER'], $ldap_server_conf_item['LDAP_BIND_PASSWORD'])) {
+                    $ldap_errno = ldap_errno($this->connection);
+                    $ldap_error = ldap_error($this->connection);
+                    $this->connection = false;
+                    if (count($ldap_server_conf) > 0) {
+                        ZLog::Write(LOGLEVEL_ERROR, sprintf("BackendSearchLDAP(): Could not bind to server with user '%s' and specified password (error %d: %s). Try next server.", $ldap_server_conf_item['LDAP_BIND_USER'], $ldap_errno, $ldap_error));
+                        continue;
+                    }
+                    else {
+                        throw new StatusException(sprintf("BackendSearchLDAP(): Could not bind to server with user '%s' and specified password (error %d: %s). Search aborted.", $ldap_server_conf_item['LDAP_BIND_USER'], $ldap_errno, $ldap_error), SYNC_SEARCHSTATUS_STORE_ACCESSDENIED, null, LOGLEVEL_ERROR);
+                    }
+                }
+                return;
+            }
+            else {
+                // it would be possible to use the users login and password to authenticate on the LDAP server
+                // the main $backend has to keep these values so they could be used here
                 $this->connection = false;
-                throw new StatusException(sprintf("BackendSearchLDAP(): Could not bind to server with user '%s' and specified password! Search aborted.", LDAP_BIND_USER), SYNC_SEARCHSTATUS_STORE_ACCESSDENIED, null, LOGLEVEL_ERROR);
+                if (count($ldap_server_conf) > 0) {
+                    ZLog::Write(LOGLEVEL_ERROR, "BackendSearchLDAP(): neither anonymous nor default bind enabled. Other options not implemented. Try next server.");
+                    continue;
+                }
+                else {
+                    throw new StatusException("BackendSearchLDAP(): neither anonymous nor default bind enabled. Other options not implemented. Search aborted.", SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
+                }
             }
-        }
-        else {
-            // it would be possible to use the users login and password to authenticate on the LDAP server
-            // the main $backend has to keep these values so they could be used here
-            $this->connection = false;
-            throw new StatusException("BackendSearchLDAP(): neither anonymous nor default bind enabled. Other options not implemented.", SYNC_SEARCHSTATUS_STORE_CONNECTIONFAILED, null, LOGLEVEL_ERROR);
         }
     }