I'm a big user of the Thunderbird e-mail program.
One big problem... it doesn't store or forward DXF attachments correctly. A big pain.
See:
https://bugzilla.mozilla.org/show_bug.cgi?id=215005
and
https://bugzilla.mozilla.org/show_bug.cgi?id=316795
If anyone else has had this problem, maybe we can all chip in and get a programmer to put a fix in?
-Jeff