Fix by dirkd: Since file() doesn't remove "\n" from the lines read the condition $lines[$l] == '' never evaluated to true. So $mailHeaders would always contain every line from the template while $mailBody contained none of them.

Together with the bugfix of PHP#68776 [1] disallowing multiple "\n"'s & preceding "\n" in mail()'s $additionalHeaders arg this caused mails not being sent because $mailHeaders would include at least one "\n\n" which was meant to separate the mail headers from the body.

[1] https://bugs.php.net/bug.php?id=68776

Author: Till Brehm

server/lib/classes/monitor_tools.inc.php

@@ -702,7 +702,7 @@ public function send_notification_email($template, $placeholders, $recipients) {
 		$mailSubject = '';
 		$inHeader = true;
 		for($l = 0; $l < count($lines); $l++) {
-			if($lines[$l] == '') {
+			if(trim($lines[$l]) == '') {
 				$inHeader = false;
 				continue;
 			}