I used to manage a large number of QMail installations. And because Qmail was ... weirdly licensed, I wrote a set of plugins that ran on top of a patch called Qmail-SPP. I pretty much stopped doing that years ago because life took me in other directions, and forgot all about it.
That collection is called ra-plugins and I had not touched it since late 2008.
And today... I got a patch with two whole plugins to add to it so that it makes Qmail handle email addresses more like Gmail does (aliases using user+foo and making user.foo the same as userfoo).
So, I got them, added them, fixed a few simple building issues, updated the libsmtp it uses internally for one of the plugins to a later version, and there it stays, perhaps not to be touched until 2018.