I have heard Ntop works very well on e-smith.
www.ntop.orgthere are no RPMs so you need to compile it, but it is rather simple.
It sniffs all network traffic and has a nice history report as well as bandwith utilization and overall network use stats. It's a free app thats been around a while.
You view the stats via any web browser and can add login restrictions so others cannot view the stats.
I have used it to monitor the Internet use of dual T1 bandwidth and it keeps up with the large amount of traffic and several hundred users.
I don't think it gives much info on the email history other than how much.