451 4.4.0 Primary target IP address responded with: "421 4.2.1 Unable to Connect

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C

Cary Fields

I have this odd problem. Inbound and outbound email works great except a few problem domains. When sending email from our network to two particular domains they give me 451 4.4.0 Primary target IP address responded with: " 421 4.2.1 Unable to connect." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts or, delivery failed to all alternate hosts.
And after a few days, our sending user gets a failed delivery message. I tested using Gmail, and it seems to work fine to the same addresses/domains.
The two problem domains are: spectrumse.com & environcon.com
Both of which I can telnet to the smtp server from my CAS/HUB.
Any help would be appreciated.

Thanks
 
A

Alexei Segundo

Does your CAS/HUB server connect directly to the remote Internet SMTP servers or do you have something at the Perimeter that handles your inbound/outbound SMTP traffic (e.g. Edge Server, Mimesweepeer, SendMail)? If you have a perimeter level server can you telnet directly from that to the remote SMTP servers?

Alexei
 
C

Cary Fields

There is nothing on the Outbound side, its direct. Inbound, I have a Barracuda AV/AS appliance.
 
A

Alexei Segundo

Sorry Cary, I can't think why you should be able to connect using telnet on the same box, but the Exchange connection fails. If it weren't for that I would suspect that those domains that are failing are enforcing a reverse DNS lookup on the sending (i.e. your) IP address.

Alexei
 
D

Dave Kawula - TriCon

Run your domain on mxtoolbox.com / I would also advise that it could actually be a problem on their end.

When performing your telnet testing are you doing a full test or just checking to see if your can hit port 25.

Most errors won't show until you get a little further in.

I run into issues like this all the time. If your mail server works for 95 % of outbound domains -- Odds are this:

They subscribe to a black list provider -- You are on the list

They use SPF Record Checking -- You haven't set them up

or they are using reverse lookups on your external mail alias -- and it isn't setup correctly.

If all of the above are correct -- Talk to their internal IT Exchange Admin and see if you have ended up on a spam filtering appliance on their and and ask them to whitelist you.

Hope this helps.

Thanks,

Daave Kawula Principal Consultant TriCon Technical Services Inc www.triconts.com dkawula@triconts.com www.insidetheregistry.com
 
N

Novak Wu

Have you installed Cisco PIX firewall or other firewall in your environment? If so, please refer to the following article to disable Mail Guard feature. For more information, please refer to the following articles:

http://technet.microsoft.com/en-us/library/dd277550(EXCHG.80).aspx

http://support.microsoft.com/kb/320027

Also, please navigate to the following location C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\mail.que and check the size of the file. Then, please refer to the following article to do offline defragment on mail.que.

http://technet.microsoft.com/en-us/library/aa998863(EXCHG.80).aspx

After that, please try to send the email to the target domains again.

Hope this helps.

Novak Wu
 
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