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. Restarting in 30 seconds.
If you see a lot of smtp connections or your server gets constantly in spam black lists, maybe you should check if some bot spams through your server.
The are 2 cases of spamming through a box:
1)using unsecure php forms that bots abuse
2)using smtp connection from an outside client
this artice is about the 2nd case,
Run the command telnet [host] port
for example:
-telnet mail.domain.tld 25
Right after the connection is established (more…)
here you can find various ways of sending emails with .NET 2 / .Net 1 CDONTS / Persist’s AspEmail / VB / PHP etc
You can check what connection you have via smtp protocol with the simple command:
netstat -a | grep smtp
As By default Plesk administrator’s email address is listed in: