> Actually people saying mbox is a bad database are in principle right
> (I never liked maildir either: dumping metadata into file names seemed
> to me a bit disgusting too, but I disgress). But there's something
> special about mail databases which eases that a bit: records (i.e.
> mails) are *mostly* immutable (save for some metadata), so cleverly
> written libs (mutt, dovecot) can be suprisingly good despite all.
Actually, I think the reason it works is unrelated: it's just that
people have put enough engineering efforts into making it work for large
mailboxes despite its inadequate format.
Caching, auxiliary indexes, batched-rewrites, etc... can go a long way.