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Comcast and Cox not receiving emails

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

 

Posts: 92
Joined: 16.Jan.2006
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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.
Post #: 1
RE: Comcast and Cox not receiving emails - 17.Feb.2010 12:45:45 PM   
John Weber

 

Posts: 1236
Joined: 20.Apr.2005
From: Portland, Oregon
Status: offline
when you look at the queues for those two destinations, what is the error message/failure message?

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John Weber [Lync MVP] http://tsoorad.blogspot.com

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

 

Posts: 92
Joined: 16.Jan.2006
Status: offline
Thanks John;

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

That's it!

(in reply to John Weber)
Post #: 3
RE: Comcast and Cox not receiving emails - 18.Feb.2010 12:00:16 PM   
John Weber

 

Posts: 1236
Joined: 20.Apr.2005
From: Portland, Oregon
Status: offline
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?

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John Weber [Lync MVP] http://tsoorad.blogspot.com

(in reply to TCheck)
Post #: 4
RE: Comcast and Cox not receiving emails - 18.Feb.2010 2:03:00 PM   
TCheck

 

Posts: 92
Joined: 16.Jan.2006
Status: offline
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.

(in reply to John Weber)
Post #: 5
RE: Comcast and Cox not receiving emails - 6.Apr.2010 6:38:03 PM   
boneyfrancis

 

Posts: 16
Joined: 6.Apr.2010
Status: offline
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.

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-b1y
MCSE, MCTS:E12

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

 

Posts: 87
Joined: 3.Jan.2008
Status: offline
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.

(in reply to boneyfrancis)
Post #: 7

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