"The problem is caused by the cid-uniqueness check in AttachAll(), in
combination with attachment[7] being set to 0 in AddAttachment and
AddStringAttachment."
yes I can confirm the problem is that and I solved it easily with this patch:
ORIGINAL CODE:
$this->attachment[] = array(
0 => $path,
1 => $filename,
2 => $name,
3 => $encoding,
4 => $type,
5 => false, // isStringAttachment
6 => 'attachment',
7 => 0
);
PATCHED CODE:
$this->attachment[] = array(
0 => $path,
1 => $filename,
2 => $name,
3 => $encoding,
4 => $type,
5 => false, // isStringAttachment
6 => 'attachment',
7 => uniqid()
);
this patch has to be applied to 'class.phpmailer.php' file at lines number 1236 and 1640 (methods "AddAttachment" and "AddStringAttachment")