Matt Molyneaux

Also worth noting that this would require the FSM to be thread-safe too. I think this is (accidentally) already the case with the default FSM.

There's quite a bit that needs doing here but I get the feeling that upstream is a bit dead right now. Might put some time into reviving it if I...

Wondering if this should be deferred until 4.0? I don't fancy poking around asyncore again.

Well, I would merge this PR but Github is having a moment (and has been for the last week) 

Yes, adding DKIM signatures would be a handy feature.

This might be a Centos 6 issue - it binds to IPv4 on Fedora under both Pythons 2 and 3.

Might be a result of https://bugs.python.org/issue14758

Alright, so after a bit more reading: IPv6 is only supported in Python 3 via `smtpd`; Python 2 explicitly sets `AF_INET` and Python 3 uses the first result from `getaddrinfo`...

Also, check that we can support dual-stack IPv4/IPv6. pyftplib has some code we could borrow, assuming the license is compatible

This is not actually a bug, it's just the way the underlying smtp library works.