Is your mail server an open relay?
Posted by Steve on Mon 8 Nov 2004 at 09:41
Open relays allow people to use your mail server to deliver spam and mail to people whilst using your resources.
None of the mail servers which are part of the Debian operating system are setup insecurely by default, but if you are new to setting up a mail server you should be cautious that you do not open your server accidently.
One very simple way of testing it is to fire off an automated test.
From your mail server run:
telnet relay-test.mail-abuse.org
This will attempt to connect back to your machine and run a series of mail relaying tests against it.
The success or failure will be printed at the end of the run.
If you are inadvertantly running as a relay consult your mail server documentation for tips on how to prevent it.
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D'oh.
I mistyped that by force of habbit, omit the '25' from the telnet command:
steve@skx:~$ telnet relay-test.mail-abuse.org
Trying 168.61.4.13...
Connected to Cygnus.Mail-Abuse.ORG.
Escape character is '^]'.
Connecting to 212.13.199.210 ...
<<< 220 skx.vm.bytemark.co.uk ESMTP Exim 3.35 #1 Mon, 08 Nov 2004 12:52:47 +0000
>>> HELO cygnus.mail-abuse.org
<<< 250 skx.vm.bytemark.co.uk Hello cygnus.mail-abuse.org [168.61.4.13]
:Relay test: #Quote test
>>> mail from:
<<< 250 is syntactically correct
>>> rcpt to: <'nobody@mail-abuse.org'>
<<< 501 <'nobody@mail-abuse.org'>: recipient address must contain a domain
>>> rset
<<< 250 Reset OK
:Relay test: #Test 1
...
...
...
System appeared to reject relay attempts
Connection closed by foreign host.
I'll edit the article to fix it.
-- Steve.org.uk
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I found another one that worked.
telnet rt.njabl.org 2500
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