SMTP Inbound Connections

Hello All,

I seem to have an increasing number of inbound SMTP connections each week that seem to sit idle. I don't believe external traffic to the e-mail sever has increased, in fact is should be less each month. Attached is a graph. How should I start to troubleshoot where all these connections are coming from, and if they're needed?

Netstat gives me many Port 25 connections, most of them are CLOSE_WAIT
OpManagerDisplayChart.png