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Maildir vs. mdbox

I just finished converting the largest mailbox i had. Its the service for wasteland.rfc822.org which is a receive only, no register, mail service for any anoying "we need to have your email address" services. The mailbox contained ~8.5 Million emails, in 85000 folders as Maildirs, already gzip compressed reaching back to ~2011.

The conversion with dsync took around 4 days in background on a machine with only rotating rust.

And now - compare the space savings - mostly in metadata:

root@pax:/var/vmail/...# du -sk Maildir/ mdbox/
121387420       Maildir/
44809380        mdbox/

I guess removing the old Maildir will take another 2-3 days.

One issue i found was that mdboxes need more memory opening and my imap process kept dying because the vsz was overwhelmed.

I need to increase the limit:

service imap {
  vsz_limit = 512M
}