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exchange 2003 cannot send to comcast.net

Posted on 2013-01-23
Medium Priority
Last Modified: 2013-01-24
As of 48 hours (or so) ago, mail stopped flowing to comcast.net.  The queue for comcast.net in exchange server says "an smtp protocol error has occurred".

Mail has been flowing fine to comcast for years and now i cannot get mail to go to them.

Mail to all other domains flows fine.  

No changes to nameserver since October last year, Not blacklisted.  Nothing new done on server.  

Question by:AndyMT
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LVL 12

Expert Comment

ID: 38812221
Try to telnet to their mail server from your mail server.
Also run SMTPdiag on your mail server to see what the error message is from their end. You may be blacklisted.

Author Comment

ID: 38812267
We are clean on all the blacklists.  Will telnet shortly.  Thanks
LVL 12

Accepted Solution

michaelgoldsmith earned 2000 total points
ID: 38812274
SMPTdiag will give you the error info you need to trace.
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Author Comment

ID: 38812325
Here's the results.  I had added Google's DNS servers earlier today in case the problem was there, but that made no difference.  I need education on the "serial numbers do not match".

C:\SmtpDiag>smtpdiag larry@balcombgreen.com mritrash@comcast.net

Searching for Exchange external DNS settings.
Computer name is SERVER.
VSI 1 has the following external DNS servers:,,,

Checking SOA for comcast.net.
Checking external DNS servers.
Checking internal DNS servers.
Serial numbers do not match: 2008177974  2008177972
Serial numbers do not match: 2008177974  2008177972
Serial numbers do not match: 2008177974  2008177972
SOA serial number match: Failed with one or more failures.

Checking local domain records.
Checking MX records using TCP: balcombgreen.com.
Checking MX records using UDP: balcombgreen.com.
Both TCP and UDP queries succeeded. Local DNS test passed.

Checking remote domain records.
Checking MX records using TCP: comcast.net.
Checking MX records using UDP: comcast.net.
Both TCP and UDP queries succeeded. Remote DNS test passed.

Checking MX servers listed for mritrash@comcast.net.
Connecting to mx1.comcast.net [] on port 25.
Error: Expected "220". Server is not accepting connections.
Failed to submit mail to mx1.comcast.net.
Connecting to mx2.comcast.net [] on port 25.
Error: Expected "220". Server is not accepting connections.
Failed to submit mail to mx2.comcast.net.

Author Comment

ID: 38812401
Reran the same test with the "/v".  Turns out Comcast has the domain blacklisted even though it passes every blacklist check.  Problem solved I think.
LVL 12

Expert Comment

ID: 38812933
Glad to see you resolved the issue. I suspected blacklist initially. Email them and they should get u removed within 24-48 hours.

Author Closing Comment

ID: 38814995
Even though all the normal blacklists were clean, Comcast had blocked their domain.  Running SMTPDIAG /v gave me the info I needed to resolve the situation

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