> i first learned of cyrus imap from a blogpost that FastMail folks posted, but do not much about it (other than it is highly respected as a platform for mail, calendar, contacts)...Is it built in Go?
Cyrus predates Go by quite a while! The project started in 1994. It's implemented in C.
https://en.m.wikipedia.org/wiki/Cyrus_IMAP_server
