Please see: blogpost16-WikiSuite-will-now-support-all-major-Linux-distros. While ClearOS's mail stack is powered by Cyrus IMAP, Virtualmin's mail stack is with Dovecot, so we will focus on efforts there. This page is kept for posterity.
Cyrus IMAP is the email server used in WikiSuite: https://en.wikipedia.org/wiki/Cyrus_IMAP_server
Cyrus IMAP is one of the first to support JMAP and WikiSuite is actively contributing to this initiative.