Latest LQ Deal: Linux Power User Bundle
Go Back > Forums > Linux Forums > Linux - Distributions > Debian
User Name
Debian This forum is for the discussion of Debian Linux.


  Search this Thread
Old 05-07-2005, 12:45 AM   #1
LQ Newbie
Registered: Apr 2005
Posts: 6

Rep: Reputation: 0
Open relay SMTP

I've scanned my mail server and got a warning about open SMTP relay. I'm a little confused because I read emails only trough imap. This is the list of open ports:

22/tcp open ssh
25/tcp open smtp
80/tcp open http
143/tcp open imap
220/tcp open imap3

Yes, smtp is open, but if I try to send an email trough my mail server (eg with an email address that has a different domain (eg I get an error -- no mail is relayed.

Am I missing something?
How do I find out what SMTP daemon is used?
Old 05-07-2005, 01:07 AM   #2
LQ Guru
Registered: Nov 2004
Location: San Jose, CA
Distribution: Ubuntu
Posts: 8,507

Rep: Reputation: 124Reputation: 124
Your system seems to be correctly configured: it should not relay mail for other domains. I'm not exactly sure which test was returning these results, telling you you had an open relay.
Old 05-07-2005, 02:08 PM   #3
LQ Newbie
Registered: Apr 2005
Posts: 6

Original Poster
Rep: Reputation: 0
After using some more reliable open relay tests it truns out that my SMTP is not really open; it authenticates users by domain name. I was told this could be easily spoofed but... I'm not sure how to enalbe SMPT authentication. I'm using exim and postfix. Any suggestions or pointers?

I'm not sure if its exim or postfix that's SMTP. Is there a way to find out?
Old 05-07-2005, 04:06 PM   #4
Registered: Feb 2004
Location: Southern Maine, United States
Distribution: Slackware Ubuntu Debian FreeBSD
Posts: 418

Rep: Reputation: 31
both of them.. along with about 5 others.
Old 05-07-2005, 04:34 PM   #5
LQ Newbie
Registered: Apr 2005
Posts: 6

Original Poster
Rep: Reputation: 0

BTW I found out that SMTP is postfix.
Old 05-09-2005, 05:11 PM   #6
Registered: Feb 2003
Location: Arizona
Distribution: Debian Sid
Posts: 57

Rep: Reputation: 15
to find out what it is usually all you have to do is;
telnet 25

for instance if I do it to mine I would see
220 ESMTP Postfix (Debian/GNU)

But that isn't always true, just most people have the banner turned on that way. Also, if you want a pretty good relay test for open relays. From the system you want to check do a;


the remote system will run a series of checks against the machine your are telneting from, and tell you if it can get around your configuration.
Old 05-20-2005, 10:27 AM   #7
LQ Newbie
Registered: May 2005
Posts: 1

Rep: Reputation: 0
When I tried 'telnet relay-test', I got:

Connected to
Escape character is '^]'.
/proj/maps/bin/in.relaytest: socket failed [Bad file descriptor]
Connecting to ...
Connection closed by foreign host.

(I've obscured my IP address here with

What does this indicate?


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
SMTP "open relay" and SMTP AUTH aikempshall Linux - Security 3 10-11-2006 08:19 AM
Newbie needs SMTP relay grbeck *BSD 4 03-24-2004 12:44 PM
SMTP: Relay Denied nemesisza Linux - Software 2 03-14-2004 10:54 AM
Smtp Relay john8675309 Linux - Networking 2 02-12-2004 12:14 AM
setting up a SMTP server with an "open" relay zyrtech Slackware 0 10-25-2003 09:13 AM > Forums > Linux Forums > Linux - Distributions > Debian

All times are GMT -5. The time now is 02:16 PM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration