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Old 10-07-2006, 09:48 AM   #1
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Postfix and Exchange

Iíve inherited this network and need help on PostFix. Hereís how it is currently setup.
Internet --- Firewall --- Linux (PostFix/Spam Filter) --- Exchange 2003 (SERVER1)

I have another Exchange box (SERVER2) that I want start sending mail to Postfix (SMTP Gateway) but for some reason, the Postfix is not allowing this. Mail stays on queue on this particular exchange server. The other server, SERVER1, works fine.

Is their a configuration somewhere, where Postfix will only receive mail from a particular server?

Old 10-09-2006, 10:18 PM   #2
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The main configuration file is, which is probably in /etc/postfix/. You can check the nondefault settings by running
postconf -n
To summarize your problem, and to make sure I understand it, postfix is blocking SERVER2 from relaying mail through it. The simplest way of allowing relaying is by defining either an appropriate mynetworks_style or mynetworks in If you don't understand postfix configuration, you should begin by reading Basic Configuration and Standard Configuration.

Last edited by Berhanie; 10-09-2006 at 10:23 PM.
Old 10-13-2006, 09:09 PM   #3
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One of 2 things is happening.
1. The firewall is blocking incoming connections on TCP/25 from exchange server2.
2. Postfix is blocking relaying by exchange server2.

Testing #1 is super easy.
Go to exchange server 2, open a command prompt and type
telnet ip.of.postfix 25
If you see the postfix SMTP banner in response, then the firewall is letting you through. If no response is seen and it eventually times out, then the firewall is blocking you.

My guess is the firewall is blocking you.

To test #2, execute
postconf mynetworks mynetworks_style
If mynetworks_style is not blank, then mynetworks is ignored. If mynetworks_style is set to subnet, and the exchange server2 is on the same subnet as the postfix server, then postfix is not blocking it.

If mynetworks_style is empty, then focus on mynetworks. If it's set to your entire LAN ip network "mynetworks =", then postfix isn't denying relaying. If it's set to "mynetworks =", that means only that ip can relay email thru postfix.

Let us know what you find.




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