Jan-Lukas, I read the link you recommended me. I can't see/read/modify my php.ini. I can't find such file but found in FAQ that my server provider i have website don't allow modify php.in. But I create email_test.php and test it. I have got "ok" answer. I send email to myself only and have got this same error. I don't know why it show on this line:
return (mail($this->to, $this->subject, $this->body, $this->create_header())) ? 1 : 0;
What's wrong with this line ? How fix this problem ?
Rembrandt, my email I'm sending mails are from this same domain I have website on (hope I good understand your sugesion, because I don't German)