Even if it may be possible to support asyncore/asynchat and asyncio at the same time, I would prefer to drop asyncore/asynchat support to simplify the code.

The problem is that the API will be very different.

asyncio has a different design. You don't instanciate a class to open a network connection, but you have to call "yield from loop.create_connection()" in a coroutine.

We might provide helper blocking functions starting the server for us and then running the event loop until CTRL+c is pressed (or another event to stop to stop the loop).

Rewriting smtpd with asyncio would allow to use it in an asyncio application. In 2015, I expect to see more and more applications using asyncio than asyncore/asynchat.

Can we modify the issue title to "Rewrite smtpd with asyncio"?