I've noticed recently, on my mailstores, that /var/log/system.log has the following line in it a few times per day:

kernel[0]: Limiting open port RST response from 770 to 250 packets per second

At that same time, in /opt/zimbra/log/zimbrastats.csv, the number of pop connections spikes to around 20(usually 1-5). I have also noticed the advanced client hangs a bit during this time, sometimes getting a cannot connect to server popup. Eventually waiting a minute everything is fine.

A google search of what is in system.log says it's someone doing port scanning. Our snort logs show little abnormalities at the time this happens..mainly more pop connects than usual...this can also be verified by checking out /opt/zimbra/log/mailbox.log and looking at attempted pop connections for users.

I know port scanning happens and we have a firewall in place so only the needed ports are advertised...but should I be worrying about this? It obviously is causing some performance issues for the web client. We are using Mac OS X 10.4.10 dual G5 with 4 GB mem.

Any suggestions?