Under the hood, mu4e is fully search-based, similar to programs like notmuch4 and sup5.
However, mu4e’s user-interface is quite different. mu4e’s mail handling (deleting, moving etc.) is inspired by Wanderlustu6 (another emacs-based e-mail client), mutt7 and the dired file-manager for emacs.
mu4e tries to keep all the ’state’ in your maildirs, so you can easily switch between clients, synchronize over IMAP, backup with rsync and so on. If you delete the database, you won’t lose any information.