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