Sender Domain Does Not Resolve

[jardows]

We are running Senmail 8.10 on Linux. When we try to send mail to a particular domain, we get a return message saying:

----- The following addresses had transient non-fatal errors -----
<rwjones@tren.com>

----- Transcript of session follows -----
... while talking to mail.tren.com.:

>>> MAIL From:<jmeadows@bbcnet.edu> SIZE=232

<<< 451 4.1.8 Domain of sender address jmeadows@bbcnet.edu does not resolve
<rwjones@tren.com>... Deferred: 451 4.1.8 Domain of sender address jmeadows@bbcnet.edu does not resolve
Warning: message still undelivered after 4 hours
Will keep trying until message is 5 days old

Reporting-MTA: dns; hawking.bbcnet.edu
Arrival-Date: Thu, 17 Oct 2002 15:14:40 -0500

Final-Recipient: RFC822; rwjones@tren.com
Action: delayed
Status: 4.1.8
Diagnostic-Code: SMTP; 451 4.1.8 Domain of sender address jmeadows@bbcnet.edu does not resolve
Last-Attempt-Date: Thu, 17 Oct 2002 19:31:18 -0500
Will-Retry-Until: Tue, 22 Oct 2002 15:14:40 -0500

Is this a problem on our end or theirs? All other domains (that we know of) are working.

Jacob Meadows
Network Technician, Baptist Bible College

 

[Butterfly123]

This is a problem from reciever domain end.. MAy be their DNS entry does not exists... - Hemant
NSIG,
Satyam Computer Services Ltd

 

[Stingreen]

Your reverse DNS entries must match the hostname where the email is being sent. Otherwise the remote system will not accept the mail.

 

[fluffybunny]

Hey Stingreen,

What do you mean ? Could you explain in more words ? I just got back from a lobotomy so please excuse my inability to understand.

I'm interested also, but I don't get what you mean.

Regards. ::

 

[Stingreen]

Have you ever received a SPAM into your mailbox? If your answer is yes, take sometime and check for the header of the spam you received,
It might look like this (most spammers use it)

Received : mx05.hotmail.com[64.98.145.75],

Now do you think that this email is sent from Hotmail's outbound mail servers?
Nope, not at all.That hostname you're seeing above is the hostname of the &quot;sender&quot; doesn't mean that it's the real hostname which it supposed to be. On other words, it can be faked very easily. However, the IP itself is where you should be looking into..

Now, if we go back the question you asked,
Simply, telnet into a mailserver's 25th port and watch it's banner which should give you a hostname right?
But there is also a reverse DNS address for every particular IP address.( well, in some cases not) That's what some mail servers are checking. They simply try to match the hostname on the greeting message and the hostname from the Reverse DNS. If they don't match, that means email is relayed from another server ,then mail server will not accept the mail.
In our example, 64.98.145.75( IP above)'s reverse DNS is not mx05.hotmail.com, that means, this email is not relayed from hotmail's outbound server as you thought as it should be.
For an example, Our universities( columbia.edu), mail system is using reverse DNS for basic spam check.
Try to send an email to whateveryoulike@columbia.edu
If your SMTP's hostname is not matched to your reverse DNS, then the mail will bounce back saying &quot;Domain name must resolve&quot; which is translated to &quot;Check your reverse DNS&quot;
If you get an error like &quot;Unknown user&quot;. Than that means your mail has passed the first test ( which reverse DNS) but now couldn't find the user you intented to send.

This is a pretty brief explanation on how it works, configuration is whole another question.
Hope that helps.

 

[fluffybunny]

Thanks Stingreen. That explaination helped a lot. I am also having some problems with some domains not being able to send email to my site. Errors that users of other sites receive is that domain not found or host not found or some effect like that. Thing is only some sites are having this problem. Others are able to send mail to my site.

I have a feeling that this may be due to DNS issues. Thing is I am not sure what the problem is.
Could any of you guys point me to some site where I can get a clear understanding of configuring DNS / Reverse DNS.
DNS on my site works, however Reverse DNS is another matter. When I do an nslookup using another server in another domain to lookup my site using reverse lookup, I get an error. How do I solve this issue ?

Also another question : is the latest book by Cricket Liu DNS & Bind Cookbook by O'Reilly good or not ? Have any of you looked at it ?

Regards.

 

[jardows]

Well, the reverse DNS seems to be setup fine. Just in case, what is some good ways to check?

 

[yahoo16]

Hi jardows,

I have a similar kind of problem in my server too. It doesnt receive mail from other domains. What could be the problem ? My DNS and Reverse DNS entries are fine. I'm running Sun 9 OE with sendmail 8.12.2.

Can u suggest some thing which wud fix my problem. Sending mails to other domain is working fine.

Awaiting ur kindest reply.

yahoo16