Comcast and Cox not receiving emails (Full Version)

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TCheck -> Comcast and Cox not receiving emails (17.Feb.2010 12:32:38 PM)

We have a server that is able to send to all ISP's except Comcast and Cox. We have called both Comcast and Cox and they say we are not blocked but when we send an email to an email at these ISp's we get;
XXXXX@comcast.net
Microsoft Exchange has been trying to deliver this message without success and has stopped trying. Please try sending this message again, or provide the following diagnostic text to your system administrator.

Any ideas on how to resolve this would be appreciated.



John Weber -> RE: Comcast and Cox not receiving emails (17.Feb.2010 12:45:45 PM)

when you look at the queues for those two destinations, what is the error message/failure message?



TCheck -> RE: Comcast and Cox not receiving emails (17.Feb.2010 7:29:42 PM)

Thanks John;

The message is "Last Error: 400 4.4.7 Message delayed"

That's it!



John Weber -> RE: Comcast and Cox not receiving emails (18.Feb.2010 12:00:16 PM)

can you do a manual dns / nslookup of those two domain and then connect manually via telnet?

When I have seen this before, where only SOME domains can't be sent to, you have a DNS lookup issue.

Do you have forwarding on your DNS server? Which DNS source is your Exchange Server (HT or Edge) using? Can you do a manual connection?



TCheck -> RE: Comcast and Cox not receiving emails (18.Feb.2010 2:03:00 PM)

when we telnet to mx1.comcast.net we get a 554 error code "imta01.westchester.pa.mail.comcast.net [External IP] dnsBLs http://help.comcast.net/content/bl0010 cloud mark intel csi".

It looks like we are black listed but when we call Comcast they say we are not.

Not sure which DNS source is the Exchange Server is, how can i check?

Thanks.



boneyfrancis -> RE: Comcast and Cox not receiving emails (6.Apr.2010 6:38:03 PM)

I'd suspect a RDNS misconfiguration issue here.
Check: http://postmaster.aol.com/tools/rdns.html, and verify that your public IP has a valid PTR/txt/Reverse-DNS record pointing to your mail server.



thehutch -> RE: Comcast and Cox not receiving emails (8.Apr.2010 1:12:56 PM)

What boneyfrancis and John said! At this point you may want to contact your ISP and ask to a different primary DNS server address to use for mail routing or try using a third party DNS solution.



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