Ok, i solved the problem. In Version 2.1.4 are some functions in functions.inc.php which don'work very well. I replaced the functions

function my_strpos($haystack, $needle, $offset=0, $encoding='utf-8')
function encode_mail_name($name)
function mail_header_filter($string)
function my_quoted_printable_encode($sText, $bEmulate_imap_8bit=true)
function my_mail($to, $subject, $message, $from='')

of the current version functions.inc.php 2.2.6