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Old 06-07-2004, 03:59 AM   #1
Registered: Jul 2003
Location: Norway
Posts: 65

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Question Sendmail relay denied. PTR or IP lookup failure.

Hi. I have Fedora Core 1, and I think that my mail server is allmost setup right. I have a fixed IP with an ISP, and bought a domain ( where I set the MX records pointing to

From the local area network all works. I can send to hotmail, receive from any machine on the Local Area Network etc.
Also my pop works. I can receive my mail using windows outlook express from work.

But the problem is when trying to use the mail server from work (, fixed IP with as domain) or my brothers computer (he uses as ISP, and don't have a fixed IP or a domain. This day the IP was . The logs give me the following (first from my brothers place, then from work):

Jun 6 12:00:38 linux sendmail[7960]: i56A0aLj007960: ruleset=check_rcpt, arg1=<>, relay=[], reject=550 5.7.1 <>... Relaying denied. IP name lookup failed []

Jun 7 10:13:53 linux sendmail[12848]: i578DrLj012848: ruleset=check_rcpt, arg1=<>, relay=[], reject=450 4.7.1 <>... Relaying temporarily denied. Cannot resolve PTR record for
From these newsgroups, I got a little confused. Some says I have lists the IP address in /etc/mail/relay-domains or /etc/mail/access (or maybe both??). This would fix sending mail from work, which has an fixed IP. Right?

But what about sending mail from my brother, where the IP changes often. I gave him an account called and he can send to users of my system (, and can receive via pop from anyone, but cannot send to, say, hotmail as seen in the log above. Can I insert in either "relay-domains" or "access" so that he can mail too. Or is it another way of so that he can send mails using my server and domain (that don't fail any junk mail filters and won't make my server an open relay)? Or can I use the linux username and password somehow to authenticate that it is him and none other trying to relay a mail via my system?

Hope you can help
Old 06-09-2004, 01:59 PM   #2
Registered: Jul 2003
Location: Norway
Posts: 65

Original Poster
Rep: Reputation: 15
Found a couple of solutions, and now it works.

Apparently the file /etc/mail/access is alpha and omega when dealing with sendmail relay. A button called "spam" in webmin (for RedHat and Fedora anyway). But this only works good with fixed IP addresses (not any good for dial ups). An even better way is to use the AUTH features of the latest sendmail version (8.12.xx). All this was explained at (by an expert, so a newbie like me had a hard time following (and then discovering RedHat had allready done most of it anyway, so it was no need for me to do much at all. )) All I had to do was follow this user guide (For RedHat and Fedora users):

Another guide highly recommended (but I allready had my system working, so I have not tested it):

I was thinking about encrypting the pop or imap too, but then this was posted:

"Ironically, your brother isn't a security concern, since you can't "sniff" the internet. He could send his username and password to your server in plain text, and it would be completely secure. The only place it could be sniffed is on your network or his. Which would require either his machine or your server to already be compromised (or at least a machine on either network). If this is the case (hijacked machines on the LAN) usernames and passwords are the least of your concerns.".
Since neither my brothers "network" or my network is being used by others then me or him (we both use ADSL ISP with one to two computers), this would not be an concern, so I guess pop3 using normal port 110 would suffice. And I have heard MS outlook express and POP3 have troubles enough with the certificate we create using one of the methods above, so why push my luck...


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