Check that your server is not on any RBL list (real time black hole list).

Alternately set up a smart host to send through a provider they don't block (like gmail/google apps for domains).
You can test manually using telnet.

First get their mail exchange records:

nslookup -query=MX comcast.com
Server: x.x.x.x
Address: y.y.y.y#53

Non-authoritative answer:
comcast.com mail exchanger = 5 mx1.comcast.com.

comcast.com mail exchanger = 5 mx2.comcast.com.

comcast.com mail exchanger = 5 mx3.comcast.com.

comcast.com mail exchanger = 5 mx4.comcast.com.

Authoritative answers can be found from:
comcast.com nameserver = dns101.comcast.net.

comcast.com nameserver = dns102.comcast.net.

comcast.com nameserver = dns103.comcast.net.

comcast.com nameserver = dns104.comcast.net.

comcast.com nameserver = dns105.comcast.net.

mx1.comcast.com internet address = 76.96.32.247

mx2.comcast.com internet address = 76.96.32.252

mx3.comcast.com internet address = 69.241.43.117

mx4.comcast.com internet address = 69.241.43.118

telnet 76.96.32.24 25

helo <your server name>
mail from:<user>@<your server name>
rcpt to:<user2>@c omcast.com
This is a test email
.

On Wed, Nov 21, 2012 at 4:50 PM, keith smith <klsmith2020@yahoo.com> wrote:

Hi,

One of the Vhost on a server I run is a shopping cart. We have been experiencing bounced emails when sending to Comcast. We do not have this problem with any other ISP.

These emails are sent directly from the box, such as the order confirmation email.

The problem started when we upgraded from CentOS 5.x to CentOS 6.x. I wonder if anyone else has experience this problem.

The failure message:

> Hi. This is the qmail-send program at [boxes fully qualified domain name].
> 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.
>
> [customers email address]:
> CNAME lookup failed temporarily. (#4.4.3) I'm not going to try again;
> this message has been in the queue too long.

Only happens when emails are sent to Comcast directly from the server - order confirmation and shipping confirmation.

I've search for a solution and read this can be corrected by setting the DISABLE_CNAME_LOOKUP in qmail-remote. Something about a buffer being too small??

Is this true or could it be another issue?

Thank you for your feedback!

Keith

------------------------
Keith Smith

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