Fork to py3 with asyncio

[icgood]

https://docs.python.org/3/library/asyncio.html

[icgood]

It seems unlikely that this will happen. Python2 is alive and well, and a significant rewrite of slimta would probably be in a new language entirely.

[brycedrennan]

@icgood how you feeling about this 4 years later?

[icgood]

@brycedrennan actually, only in the recent release of Python 3.7 they've finally added a feature that un-blocks an asyncio rewrite: asyncio.loop.start_tls(). The ubiquitous STARTTLS command was essentially impossible to implement prior to 3.7.

Another question mark for me is the perceived difficulty of porting all the unit tests, which rely on the older and mostly deprecated mox3 library. However, many of the tests use mock sockets, which should transition nicely to something like this.

It's something I want to do, of course, but time is the limiting factor.