[Dovecot] IMAP traffic logging

Hi! Is there any known way I can log traffic caused by IMAP sessions? First it is adequate to have a rough overall statistic let's say traffic per hour - this is easily done with iptables. But on the long term I also need information on account basis.

I thought of rawlogging every IMAP session and then simply count the filesizes. But the created logs have dropouts because dovecot doesn't log whole FETCH commands what is a problem.

Thanks for every idea you have!

Paul