We have to setup a server which gets a copy of all messages send and received by our mailserver as a 1:1 copy. Mails send to multiple recipients should be calculated and saved per user. (great if you usually have lost of mails send to groups of people.)
So no duplication should be used here. (e.g. save the message and refer the different recipients to it.)
How can I calculate the current traffic in the best way to extrapolate the amount of space to be planed for the new server?