xinetd[#]: Deactivating service smtp due to excessive incoming connections. Restarting in 30 seconds.

This happened to a Plesk 8.x Linux (RH) server, the problem was that smtp service was up and running, and the queue was very light , but smtp wouldn’t accept any connections at port 25 even from localhost. In the /var/log/messages I saw this disturbing message: xinetd[#]: Deactivating service smtp due to excessive incoming connections. ...

Smtp Connections list

You can check what connection you have via smtp protocol with the simple command: netstat -a | grep smtp

How to Prevent the IIS SMTP Virtual Server from Relaying E-mail Messages

Do the following: 1) Start Internet Information Services Manager or open the Internet Information Services (IIS) snap-in. 2) Expand Server_name, where Server_name is the name of the server, right-click Default SMTP Virtual Server, and then click Properties.