I’ve been using
as my MUA for over 8 years now.
Long ago I would ssh to my server and run it on local Maildirs, but as soon as I
started using smartphones and multiple computers I had to switch to an IMAP+SSL
header_cache option has long made accessing large mailboxes snappy, and
message_cachedir option available in 1.5 makes browsing through
messages with attachments equally snappy over IMAP.
A useful side effect of message body caching is that it provides an offline copy of entire mailboxes which get synchronized automatically and can easily be read in Mutt as a local mailbox… well, almost.