My email programs of choice are MDaemon for the server and K-9 Mail, Outlook, and Opera Mail for the client. K-9, in particular, has the highest-quality IMAP implementation I have ever seen. I wouldnβt recommend MDaemon or Opera Mail to others, because one is expensive and the other is unmaintained, but they work great for me.
I have also tried Thunderbird, Postbox, Kerio Mail Server, and Exchange, but they didnβt fit me as well.
Over Christmas, I upgraded my MDaemon server from a fairly old version. The biggest improvements I saw were the addition of TLS 1.2 and a vendor-provided spam protection service (that complements the existing local SpamAssassin). There were a few bumps along the upgrade path around service startup dependency ordering, spam database migration, username format changes, password hashing changes and DoS protection, but I got them all figured out and now itβs rock solid again.
This is the new server hosting MDaemon for me, running clean and green in my parentsβ house.