Sure, MongoDB does manage files but for the email app this is behind an abstraction and possibly in a different machine. I was more referring to maildir/mbox wh

Sure, MongoDB does manage files but for the email app this is behind an abstraction and possibly in a different machine. I was more referring to maildir/mbox where the email server has to write and read files while juggling with user/group permissions, invoking shell and such. WildDuck just writes and reads stuff from a database like a regular web server software.