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Community ▶ Questions ▶ comcast.net rejecting e-mail from my server
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comcast.net rejecting e-mail from my server

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Hi,

I moved my e-mail server (qmail) to linode a few weeks ago. Sometime after I moved it, comcast began rejecting e-mail from my server. Here's a typical bounce:

Hi. This is the qmail-send program at jfoo.org.

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.

<xxxxxxxx@comcast.net>:

CNAME lookup failed temporarily. (#4.4.3)

I'm not going to try again; this message has been in the queue too long.

I managed to get an e-mail to support, but after promising to look at it, I have not heard back.

Anyone else? Any ideas? Reverse DNS for my server is set to mail.jfoo.org, and my server is mail.jfoo.org (and has an alias for www.jfoo.com)

Is this related to Linode's address space? Or is comcast just picky about who they'll take e-mail from? (I am not a spammer, this is my home project server, very low volume)

Thanks,

John

5 Replies

97.107.136.8 reverses to mail.jfoo.org, which is a CNAME for www.jfoo.com, which is a CNAME for jfoo.com. Additionally, the first MX record for jfoo.org is a CNAME, which is a RFC violation.

Try ditching the CNAMEs and just use A records – it will make DNS resolution a bit faster in general, and will avoid inadvertently running into situations where CNAMEs are contraindicated.

The MX records are not supposed to point to a CNAME record. It looks like you have all kinds of loops going on there. You should pick a name for your mail server like mail.jfoo.com or mail.jfoo.org and stick with it. Set that name as an A record. You can have more than one A record to an IP address, but only one name can be set as a reverse. Using A records instead of CNAMEs will also save on DNS lookups.

What you have..

jfoo.org. 2408 IN MX 0 mail.jfoo.org.

mail.jfoo.org. 3573 IN CNAME www.jfoo.com.

www.jfoo.com. 3573 IN CNAME jfoo.com.

jfoo.com. 2253 IN MX 0 mail.jfoo.org.

You should really have..

jfoo.com. IN MX mail.jfoo.com.

mail.jfoo.com. IN A 97.107.136.8

jfoo.com. IN A 97.107.136.8

www.jfoo.com. IN CNAME jfoo.com.

jfoo.org. IN MX mail.jfoo.org.

mail.jfoo.org. IN A 97.107.136.8

jfoo.org. IN A 216.243.177.235

www.jfoo.org. IN CNAME jfoo.org.

That's just an example.

Thanks. I created an A record for mail.jfoo.org, that might take care of it. The chain of aliases was mostly from being lazy with godaddy's DNS tool and transferring things from the old server to the new one piece at a time. Once everything is transferred, I'll go back and clean up the DNS.

Thanks again…

j

Another resource for Comcast mail issues is:

http://postmaster.comcast.net/

Although in this case it is probably the DNS/rDNS configuration as already stated.

Thanks, I think it is now resolved.

The A record didn't do the trick, which makes sense, since comcast was rejecting mail FROM me, not sending mail TO me.

I had already checked the postmaster.comcast.net page carefully, no help there.

And then, mostly through a chance e-mail on the qmail mailing list, I found that the error message I was getting indicated a problem with DNS replies being too large. There's a patch for qmail for that, I installed it, and things seem to be working again. I didn't do any serious testing, so it's also possible that it was just chance…

Thanks for the replies

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