Since Dovecot 2.4 is dropping replication, I'll definitely need to rework my mail servers and those for BSDMail. I think I'll be going back to Cyrus, which I last used over 20 years ago. The problem is my memories have long faded, so it'll be like studying it again from scratch. And that makes me happy, because it'll be like learning something totally new!
Special thanks to @h3artbl33d for the heads up!