kudos for the book. I really liked it. Will/Could you add a section for Dovecot also?
I don't believe I will be doing a Dovecot chapter anytime soon, for the reasons I stated at the beginning of http://gogs.info/books/debian-mail/chunked/courier.html
But, I must admit, I really like Dovecots Sieve filtering.
I do plan to publish the books Docbook sources on Github, hopefully someone who has more experience with Dovecot would be interested in contributing.