There is a problem with Turkish characters in the mail header.

[Seditio CMS]

The e-mail we sent turns out to be corrupt in Turkish ???? in this way
İıçöğü problem

[Seditio CMS]

Solved
smtp.mail.connector.php

find
$smtp_from_title = (!empty($smtp_from_title)) ? $smtp_from_title : $cfg['maintitle'];
add
$smtp_title = "=?".$cfg['charset']."?B?".base64_encode($smtp_from_title)."?=";

find
$mail->setFrom($smtp_from, $smtp_from_title);
change
$mail->setFrom($smtp_from, $smtp_title);