fixes #3658

Closes #3658

Merge request studip/studip!2616

config/config_defaults.inc.php

@@ -199,7 +199,7 @@ $MAIL_TRANSPORT = "smtp";
 ----------------------------------------------------------------
 leave blank or try 127.0.0.1 if localhost is also the mailserver
 ignore if you don't use smtp as transport*/
-$MAIL_HOST_NAME = "";                               //which mailserver should we use? (must allow mail-relaying from $MAIL_LOCALHOST, defaults to SERVER_NAME)
+$MAIL_HOST_NAME = "";                               //which mailserver should we use? (must allow mail-relaying from $MAIL_LOCALHOST, defaults to localhost)
 $MAIL_SMTP_OPTIONS = [
     'port' => 25,
     'user' => '',

lib/bootstrap.php

@@ -269,8 +269,8 @@ $mail_transporter_class = $mail_transporter_name . '_class';
 $mail_transporter = new $mail_transporter_class;
 if ($mail_transporter_name == 'smtp_message') {
     include 'vendor/email_message/smtp.php';
-    $mail_transporter->localhost = ($GLOBALS['MAIL_LOCALHOST'] == "") ? $_SERVER["SERVER_NAME"] : $GLOBALS['MAIL_LOCALHOST'];
-    $mail_transporter->smtp_host = ($GLOBALS['MAIL_HOST_NAME'] == "") ? $_SERVER["SERVER_NAME"] : $GLOBALS['MAIL_HOST_NAME'];
+    $mail_transporter->localhost = $GLOBALS['MAIL_LOCALHOST'] ?: $_SERVER['SERVER_NAME'];
+    $mail_transporter->smtp_host = $GLOBALS['MAIL_HOST_NAME'] ?: 'localhost';
     if (is_array($GLOBALS['MAIL_SMTP_OPTIONS'])) {
         foreach ($GLOBALS['MAIL_SMTP_OPTIONS'] as $key => $value) {
             $mail_transporter->{"smtp_$key"} = $value;