When attaching an application/octet-stream Content-Type, the roundup
mailgw should leave the attachment unchanged, in particular it should
not try to transcode to utf-8.

I'm observing a transcoding of an application/octet-stream attachement
(in latin-1 encoding).

I'll try to come up with a test for this.

Note that this worked (was not transcoded) in 1.6.0 (before the changes
to the mail gateway).

I'm testing with python2.7 but assume this also happens with python3

Joseph, hope it's ok for you that I've put you on nosy.