A friend of mine just told me that he can't send mails to accounts on one of my servers via the SMTP server provided by his ISP.

The error message in the bounce he gets reads:

Hi. This is the qmail-send program at aon.at.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

CNAME lookup failed temporarily. (#4.4.3)
I'm not going to try again; this message has been in the queue too long.

Any ideas what could be the reason for this?

I have double-checked the DNS records for my domain, but they seem perfectly fine, and from any other mail servers I tested, delivery works flawlessly…


In short: qmail is b0rked. It chokes on DNS packets over 512 bytes and sends queries of type ANY which produces the largest replies to find MX records. Apparently you have a lot of information in DNS. Actually it's your friend's problem, he should apply a qmail patch, but it's fairly common, Yahoo seems to have this problem as well. Here's the long version: http://www.google.com/support/forum/p/Google%20Apps/thread?tid=34f43e3e3c59b834&hl=en


More than four months later, I finally found a solution:

The problem was that my DNS hoster somehow managed to misconfigure the zone for the specific domain so that the server would no longer respond to ANY request, but still handle all other request correctly.

Thus, qmail failed to deliver mail to my domain, because it (incorrectly, as far as I know) relies on ANY requests being answered, while all other (conforming) MTAs worked fine...


Your server should receive incoming messages. Proplem appears to be on his end. Check your postfix logs.

Checked outbound as well.

PTR record for your mail server is broken; it does not point to mail.klickerverbot.at. Error reported is incorrect, but behaviour is reasonable spam rejection behaviour.

Try using your suppliers mail server as a smarthost to send email. Depending on your email software you may be able to do this for specified domains, instead of all domains.


The error suggests that the MX records for your domain aren't hostnames (A records) but CNAMEs. If so that's against the RFCs and the reason for your problems.

If that isn't the case, knowing the domain name would help.

Using the tools at MX Toolbox doesn't show any problems. The error may well be with your friend's ISP, particularly if you don't have this problem from other senders.

  • This is not the case: The domain in question is klickverbot.at, the MX record points to mail.klickverbot.at, which has a regular A record. – dnadlinger Oct 9 '10 at 18:06
  • Maybe I've missed something obvious, though, so I'd appreciate if you could have a short look at the records for the domain. – dnadlinger Oct 9 '10 at 18:07
  • Your domain configuration looks fine from here. – Alnitak Oct 9 '10 at 18:40
  • Okay, perhaps the other ISP is really at fault. The reason I'm not quite sure about that is that the ISP in question is (or at least was once) the biggest one in Austria. I guess I'll drop them a line… – dnadlinger Oct 9 '10 at 19:25

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