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421 4.4.2 Connection Dropped only on a few domains

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421 4.4.2 Connection Dropped only on a few domains - 14.Feb.2013 10:15:33 AM

ChrisCaldwell

Posts: 2
Joined: 17.Dec.2012
Status: offline

I have been troubleshooting this issue long enough that it makes me want to take a gallon of gas and a match to my Exchange server.

I have 8 domains that I cannot send email to. When I view the queue viewer I show six of the domains returning "451 4.4.0 Primary target IP address responded with: 421 4.4.2 Connection dropped. Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts."

Another one of the queued messages says "451 4.4.0 Primary target IP address responded with: 421 Refused. Your reverse DNS entry does not resolve. Attempted fail over to alternate host blah, blah, blah"

We use a hosted Barracuda solution but at some point in the past we were being hammered with spam that was being sent via direct smtp transactions to our IP which bypassed our hosted Barracuda. So we put a firewall rule in place to only accept smtp from the IP address of our hosted Barracuda. Spam issue resolved but I was beginning to wonder if this was contributing to some of our problems. Since we were limiting smtp I could not even telnet into my server for testing. So I have removed the smtp limiter rule from my firewall.

I have verified without any doubt at all that my PRT record is correct. I have successfully connected via telnet session from multiple locations. I have run many, many, many tests on mxtoolbox.com and everything comes back showing that PTR is correct and there are no issues.

I ran the mailflow troubleshooter to collect some more data. One of the domains that I cannot deliver to shows the following mail acceptance failure: "Remote server mailfilter.onlymyemail.com failed the mail acceptance test. RCPT TO command: Respond = 550 mydomain.org is not filtered/routed by this server". Another one of the domains that I cannot send to shows this mail acceptance failure: "Remote server mail.othercompany.org failed the mail acceptance test. RCPT TO command: Respond = 553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)". The last is the one I see most often in the mail flow troubleshooter.

What could I be missing? Any help would be appreciated, I'm ready to starting pulling my hair out over this issue.