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I have set up an ISPConfig server to host email for several domains and I am having a problem with mail sent from this server not being delivered to some, but not all, valid domains.

When mail is rejected, it contains an error message similar to the following:

recipient@comcast.net: Host or domain name not found for name=comcast.net Type=A: Host found but no data record of requested type

I thought that my domain may have gotten blacklisted, but I didn't find any listings when checked the domain against several BLs.

AFAIK, Type A records are IPv4 addresses and should always exist if a DNS record exists.

I'm at a loss.

Can anyone shed some light on what this message is telling me?

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No, you can have an existing domain name with no A records. –  bortzmeyer May 15 '09 at 20:34
    
Also, when delivering mail, postfix will look for MX records that match the @domain part of the email address, to discover the mail server that handles mail for domain. –  Dave Cheney May 17 '09 at 12:45
    
Also, you said the error message is "similar to". Do not post such crap. Post the ACTUAL error message, debugging is hard enough, no need to make it more difficult by posting "similar" messages. –  bortzmeyer May 18 '09 at 6:42
    
Normally, I would have cut and pasted the whole error message, but I needed to anonymize the email address to protect the innocent... –  Jeff Leonard May 18 '09 at 14:14

4 Answers 4

There are A (and MX, too) records for comcast.net. Therefore, I strongly suspect a DNS issue. You should debug your DNS resolver first. For instance, what do dig A comcast.net or dig MX comcast.net yield?

If the problem is temporary, then you'll have to perform the dig when the problem occurs.

And, no, it is perfectly legal to not have A records.

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Some of the bigger ISP's will look for a PTR record...they will not allow email..

further they will have a second line of spam filters that will check for an A record. It might be legal to not have an A record, but is a good idea too have an A record for the relay.

On my brightmail servers I have made the decision to not accept mail if an A record is not found. I have not had any reports from the business that they are not able to transact email for any reason.

Verizon and Comcast have the tightest rules that I have found.

I also use optus looking glass (that is my google term I search for) to check to see what I look like DNS wise from the outside world.

Lastly...you might get past some very tight servers if you use a proper SPF record.

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Although the OP did not provide many details, it seems the error message was locally generated and therefore has nothing to do with Comcast's rules or checks. –  bortzmeyer May 18 '09 at 6:43
    
What does your DNS setup look like? and who are you using for your outside DNS servers? –  Thomas Denton May 18 '09 at 11:12

I am not sure if it is related to the specific error you are having, but I had a similar issue with Postfix and Comcast related to Reverse DNS lookup.

Ensure your domains are set up for reverse lookup, and give it another shot.

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Absolutely no connection with the error message he got. –  bortzmeyer May 15 '09 at 20:31

You're trying to resolve an address as a domain. While you can do that, there is no guarantee that you'll get what you're after. What you really want is for your MTA to pick up the MX record for comcast.net, and not just resolve to comcast.net.

Also, it sounds like you're attempting delivery to the MTA at a server named "comcast.net", but I suspect you really want to attempt delivery to smtp.comcast.net instead. I'm sure you'll have a bit more luck with that address.

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