If you have the problem, that the size of the attachments are all only 8K, I think here is a small solution.
change the file: ../program/lib/Mail/mime.php
change this line: $cont = fread($fd, $filesize);
to: while ($info = fread($fd,8192)) {
$cont .= $info;
}
it seams that this is the size of the apache buffer that makes the problem.
have a nice day