At the moment I am currently writing an IMAP server in Erlang (google Erlang IMAP and you'll find me pretty fast) and the IMAP protocol is crazy complicated.

Although after you get far enough into the syntax you start to see why the protocol is as complicated as it is. The protocol itself is written as a series of design patterns so each command had a predictable request pattern and a response pattern. After you get past the initial parsing of the command and response strings the protocol become much easier IF you think of them as a series of patterns.

People who work on email systems say IMAP is one messy protocol to deal with. Still, arguably, gives you better features than anything else. Email needs improvement, but it's not an easy task. I am also surprised to see Google implement it after all. I expected that the world would move on to something better eventually. I don't expect this to happen fast though. Migrating email systems is a slow process that regular people and system administrators find painful.