logging download speed for services

Jan 23 07:14:13 srv dovecot[7702]: imap(something): session=, Logged out bytes=189/2669 Jan 23 07:14:57 srv dovecot[7702]: pop3(abc): session=<X7tLd2tjeeSy7wrl>, Disconnected: Logged out top=0/0, retr=0/0, del=0/0, size=0, bytes=12/43

Could dovecot be logging download speed for these and log it? (ignoring idle times for imap and only counting fetches etc)

The goal is to be able to compare users speed, notice degradation and other such problems.

-- Arkadiusz Miśkiewicz, arekm / ( maven.pl | pld-linux.org )