unable to set gid=33

...
2019-07-13 09:14:44 unable to set gid=33 or uid=0 (euid=0): forcing real = effective
2019-07-13 15:38:11 unable to set gid=33 or uid=0 (euid=0): forcing real = effective
...

Reproduction:

mailtest.php

<?php
    $email = "w.nizinski@grinn-global.com";
    $subject = "test z phpa";
    $message = "lorem ipsum";
 
    $mail = \mail($email, $subject, $message);
    print ($mail);
?>