> I've attached a patch that migrates from the rfc822 module to the email
> module for files that import it:

Cool John!

> A lot of the message strings in the tests seem to have headers defined
> twice (ie. 'FROM:' & 'From:', 'TO:' & 'To:'), and the behaviour for
> parsing these seems to be different between the rfc822 and email
> modules. I'm not sure if the duplicate headers were originally
> intentional - to comply with how the rfc822 module works - or not.

see issue2550869 it seems this is unwanted behaviour, the rfc822 module
was used in a way that the duplicate headers were not discovered in
test_mailgw.py.

> The second thing is that the 'roundup/mailgw.py' seems to use the
> mimetypes module to generate outgoing emails. This is another deprecated
> module that should probably be replaced with the email module.

Yes, I also saw that mimetypes (und mimetools) should do away.
Thanks for the progress!