As of Friday I am having certain emails inbound and outboud that are failing to send or recieve. The ones that are failing to send I can observein the queue. I ran the Troubleshooting agent and it comes up with warnings about ping unsucessful to the hosts of the mail records. But the warning seems wrong I can ping or nslookup all thes host records with no problem from that machine, my router or any of the domain controllers. I can also send that same email from any online webmail account to these companies with no problems and they can reply to those with no problem. This seems to be specific to our Exchange server corporate E-mail. Has anybody had any problems like this or can me a few suggestions. All of my searching on the web has lead me to articles suggesting different possiblites that either do not apply or are really vauge about why an email would get stuck in the queue. Are there any other tools that I can add on that might be able to troubleshoot my mail flow problems. I am looking for something that can say you have a problem at this hop or at the nameserver or something. Not just connection dropped with an error number that can mean about 900 differnt things.Thank You,Mike

I would first try telnetting to remote domain from exchange box and see i have good connectivity and firewall is not causing any issue XFOR: Telnet to Port 25 to Test SMTP Communication http://support.microsoft.com/kb/153119 Also check below Mail Flow Troubleshooter in Exchange Troubleshooting Assistant (ExTRA) - A closer look http://msexchangeteam.com/archive/2006/08/07/428616.aspx Troubleshooting Exchange 2007 Transport Queuing Problems http://www.exchangeninjas.com/troubleshootingexchange2007transportqueuingproblemsVinod |CCNA|MCSE 2003 +Messaging|MCTS|ITIL V3|

Thanks for the reply, I went through testing the SMTP kb article http://support.microsoft.com/kb/153119 and everything checks out fine on these email servers in question. I also went through http://msexchangeteam.com/archive/2006/08/07/428616.aspx and it basically tells me what I already know that this email is not going through due to the connection being dropped. And last this article http://www.exchangeninjas.com/troubleshootingexchange2007transportqueuingproblems is good at explaining how to find your problem using the command shell but yet again I know the error but not why it is happening. These servers all check out fine and they all can receive mail from any other mail server but ours. We send hundreds of emails a day with no problem to other servers. But for some reason as of last Friday there are certain email servers that will not accept mail from us. I have checked to make sure we have not been blacklisted on several websites and that does not appear to be the case. I am sure there is some common denominator to all these servers and why thy are being dropped. I just don't seem to be getting enough detail from these troubleshooting tools. Most of the results seem to be very broad and general. For example: your connection was dropped but no reason why it was dropped. If you know of any other articles please send them my way. I will run through anything to get this issue resolved. Thanks Again, Mike

So, the mail flow failure only happened on last Friday, wasnt it? Does mail flow only fail with certain external domains, or all external domains? Now, you can retrieve the MX record of those external domains, and also telnet to send test mail, right? Can you post all exact error info?James Luo TechNet Subscriber Support (http://technet.microsoft.com/en-us/subscriptions/ms788697.aspx) If you have any feedback on our support, please contact tngfb@microsoft.com

It started last friday but still continues.Just certain external domains, most mail is going out fine.I was able to retrieve the mx record for all those domains. And I was able to connect to them and test the SMTP communicaton. I also can send to those from a webmail account and they get it. So it is not like their server is down or anything.Here is some errors from one of the external servers:This one is from queue viewer: (error)451 4.4.0 Primary target IP address responded with: "421 4.4.2 Connectoin dropped." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.This is from the MS Exchange Troubleshooting assistant: (error)Remote server nigel.airmarketing.com failed the mail acceptance test. MAIL FROM command: Respond = 503 Bad sequence of commands.This is from the MS Exchange Troubleshooting assistant: (warning)Ping (Don't fragment = 'True' and buffer size = 4096) from server paraemail2 to remote server nigel.airmarketing.com was not successful. Check whether the server is operational or not. This is from the MS Exchange Troubleshooting assistant: (warning)Remote server nigel.airmarketing.com does not support the 8BITMIME verb. This will prevent routing of mails requiring the 8BITMIME extension. Please check whether the queue contains such messages.These are all bogus. That server does accept 8BITMIME. I can ping the server with no problem from the exchange server. I can telnet to the server and send them mail.But for some reason Exchange cannot. This is just one of many examples with mutiple different servers.Thank You,Mike

Please use the answer in this thread to disable the TCP chimney and Checksum offload Please disable all 3rd party software and firewall on the servers, and try to reproduce the issue Resources: 451 4.4.0 primary target IP address responded with 421 4.4.2 connection dropped (Similar case)James Luo TechNet Subscriber Support (http://technet.microsoft.com/en-us/subscriptions/ms788697.aspx) If you have any feedback on our support, please contact tngfb@microsoft.com

Well I came in today to check the queue and it is empty. Every single message has went through to every server and I have made no changes.Sofor some reasonexternalserversthat we email on a consistent basis stopped receiving mail from us for about 7 days. Now the problem appears to have fixed itself. I guess my biggest problem with this is it was random. If the whole server would have stopped delivering mail to all external servers that would have made more sense.I will keep an eye on it and make the changes you suggested if it starts happening again.Thank You,Mike

SureJames Luo TechNet Subscriber Support (http://technet.microsoft.com/en-us/subscriptions/ms788697.aspx) If you have any feedback on our support, please contact tngfb@microsoft.com