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Testing for mail server relay control
Seems that some people don't know how to test thier mail server to find out if it allows
3rd party relay. 3rd party relay is when your mail server will deliver other people's mail
who do not have any reason to be sending it through you. This is typically done by spammers
to let you pay for thier marketing, as well as to make it harder to track them down.
Who should relay through your machine? People who recieve email through your machine typically.
If you're providing network access to other people, then it should do it for them as well. For
example, if you set up a FreeBSD machine to share internet access with 20 people, then it should
relay their mail for them as well. This normally would be done by simply putting the IP addresses
of the local LAN in the list of IP's that we relay for. In sendmail, this is /etc/mail/access (hashed)
and in Postfix, this party of "my_networks" usually.
Use this utility: testrelay.pl that I wrote. Open it up in vi or pico
or joe or whatever and modify the mail server IP address to your mail server. Then run it from
a host that SHOULD NOT be able to relay. If the last response is "Recipient Ok", then you still have
a problem. If it says something like "550 - Access Denied. Relaying is prohibited", then things
are all good.
Don't worry, it doesn't actually email anyone... |
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