mails from iDempiere can not be forwarded

The mails I got from inside iDempiere can not be forwarded in my Icedove/Thunderbird. If I try it opens a new window with the forwarded mail but without any attachments. (In most mails from iDempiere the attachments are the most important parts.)

I tried google to find about that. I found enough complains that I am sure this is an issue (at least) in thunderbird and that it belongs to the mail format of the sent mail. I found noone with a real clue what happens. Perhaps sending the mail not as HTML may solve it as a workaround.