If you still want to reduce disk IO, you can also try (if you haven't already):- deliver: http://wiki.dovecot.org/LDA/Indexing - maildir_very_dirty_syncs=yes: http://wiki.dovecot.org/MailLocation/Maildir
We did switch from maildrop (and courier authd and cyrus sasl) to just dovecot (+sieve +manage sieve, a great simplification to build and maintain) and will ponder very dirty syncs. . .
