Checking a linux server for smtp open gateway

How can I check that a specific Linux server is NOT acting as an open SMTP gateway?

Ideally I would like to put in a place a regular script to check one of our boxes on a regular basis.

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brothertomAuthor Commented:
Yes, I tried this earlier but I get

x.x.x.x on port 25... Error - could not connect to server

I figured the tool was broken - can someone try this against a known working server and see if you get the same error message?

That's what you should get if it's not allowed - in your config files you should have your allowed networks, if the IP does not match, it's not allowed to use the smtp server.

I personally use this tool:
According to you smtp daemon you should also check the documentation in order to find out how prevent your smtp to act as an open relay.

If using pop3 on the same host, you could try learning about pop-before-smtp (on google) if you do not have a large ammount of users.

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