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.