[Dovecot] mbox vs maildir

[Jeff Kowalczyk]

FWIW, I used imapsync for the data migrations of a) an old sendmail server
with mbox format to a new server running postfix+dovecot, and b) and old
and busted Microsoft SBS2000 Exchange instance to a new server running
postfix+dovecot.

Worked well in both cases, and the process left the original
servers intact in case the migration hadn't gone as well.

Completely unscientific observation, but the Maildir format seems quite
responsive in the common email pattern of open the inbox, fetch the
message headers, let the filter process spam, finally read ham messages.
That has a lot to do with Dovecot's speed, of course.