Under the hood, mu4e is fully search-based, similar to programs like
notmuch and
sup.
However, mu4e’s user-interface is quite different. mu4e’s mail handling
(deleting, moving, etc.) is inspired by
Wanderlust (another Emacs-based e-mail client),
mutt and the dired file-manager for emacs.
mu4e keeps all the ‘state’ in your maildirs, so you can easily
switch between clients, synchronize over IMAP, backup with
rsync and so on. The Xapian-database that mu maintains is
merely a cache; if you delete it, you won’t lose any
information.