I've been monitoring the network traffic on our Zimbra (open source) server for a while now, and there has been at least 0.5 Mbit/sec of traffic going out the external network interface (eth0) for the last couple of weeks. This seems to be quite a bit considering how little mail our system processes.
I know that the various Zimbra processes communicate with one another via TCP, but wouldn't the traffic remain on the local system?
Unfortunately I don't have network traffic information going back far enough to compare with the last two weeks.
Any assistance would be appreciated. I can provide Zimbra or network settings if needed.
Is there a way to get stats on outgoing mail, so that I can see the amount being sent, and/or the accounts that are sending it? (In case someone is using their account to send out vast amounts of mail, which is unlikely.)