It seems Maildir is the safest mail format right now, as long as you could accept little performance and disk cost penalty.
On Wed, Apr 24, 2019 at 9:01 PM Tanstaafl via dovecot <dovecot@dovecot.org> wrote:
On Wed Apr 24 2019 04:12:30 GMT-0400 (Eastern Standard Time), Daniel Miller via dovecot <dovecot@dovecot.org> wrote:
If you've got good hardware, including a proper UPS, I'd recommend dbox (my server is presently using sdbox). With large mailboxes and file-based backups you'll benefit from mdbox. When reliability is the #1 concern above anything else - use maildir. Depending on your use SIS can have significant impact on storage requirements - but storage these days is relatively cheap.
My plan when I roll out my new server this year is to use mdbox, but put the indexes and other important meta data on a smallish volume using either ZFS or BTRFS, for the automatic self-healing capabilities (and the ability to expand it if necessary).
This pretty much eliminates the worry about data loss from index file corruption.
I haven't seen much feedback from users actively using SIS - I'd love to hear from high traffic sites with SIS experience to know if the corruption issues have been resolved. In my case there was at least a 30% reduction in space but I had too many errors - admittedly it's been a couple years since I last tried it.
I never tried it because of the problems with respect to backup/restore, and if I'm not mistaken, those problems have not been resolved.
Maybe its a design issue...
Or maybe it just isn't a high enough priority, like the missing x-original-to header in the LMTP code that will still prevent me from being able to use the otherwise much better LMTP delivery agent.