Open Relay Test

[D]

Hi all .. how could one test to see if an open relay exists on a
specific email server?

 

[Steve Holden]

Hi all .. how could one test to see if an open relay exists on a
specific email server?

I bet spammers would love someone to answer that question for them. You
wouldn't be planning spam, by any chance?

regards
Steve

 

[D]

Nope, quite the contrary..I'm looking to write a simple program for a
client of mine that will, among other things, verify that their
clients' email servers do not have open relays.

 

[Martin P. Hellwig]

Nope, quite the contrary..I'm looking to write a simple program for a
client of mine that will, among other things, verify that their
clients' email servers do not have open relays.

I usually test it like this:

martin@proxy:~> telnet mail.huygenslyceum.nl smtp
Trying 172.16.64.12...
Connected to mail.huygenslyceum.nl.
Escape character is '^]'.
220 mail.huygenslyceum.nl ESMTP Sendmail 8.12.11/8.12.11; Fri, 17 Feb
2006 10:03:46 +0100 (CET)
~> helo 172.16.64.1
250 mail.huygenslyceum.nl Hello [172.16.64.1], pleased to meet you
~> mail from: (e-mail address removed)
250 2.1.0 (e-mail address removed)... Sender ok
~> rcpt to: (e-mail address removed)
550 5.7.1 (e-mail address removed)... Relaying denied. IP name lookup
failed [172.16.64.1]

To get a more verbose explanation, google for smtp + telnet.

hth

 

[Steven D'Aprano]

I bet spammers would love someone to answer that question for them. You
wouldn't be planning spam, by any chance?

The spammers already know how to look for open relays. Unlike the original
poster, they know how to use Google. *wink*

Besides, not just spammers want to detect open relays. Many people like to
block mail from open relays.

 

[Ben Finney]

Hi all .. how could one test to see if an open relay exists on a
specific email server?

Use the Distributed Sender Blackhole List service:

<URL:http://dsbl.org/>

They have client programs to make it easy to use the service to test
mail systems for vulnerabilities:

<URL:http://dsbl.org/programs>

 

[D]

Thanks guys for the info..the DSBL client app is exactly what I
need..unfortunately the app I'm writing will be for Windows (the only
client I saw was for Linux). Do you know if there's a Windows command
line port?

 

[Christoph Haas]

Hi all .. how could one test to see if an open relay exists on a
specific email server?

My simple favorite... run:

telnet relay-test.mail-abuse.org

from the mail server in question (and be patient).

Kindly
Christoph

 

[D]

Thanks, Christoph..in order to automate this in a program (so the test
can be initiated from a system other than the mail server), I'm
thinking it could be automated (via pstools) to run on the system in
question. I'll give it a try!

Cheers,

Doug