Good day all,Question here, I have seen this question posted in various forms but none of the solutions have worked for me, so if anyone has anything else to try it would be greatly appreciated.Situation:Exchange 2003 Org, introduced Exchange 2007 server. Can send mail from Exchange 2003 server to mailboxes on Exchange 2007 with no problems. Can send mail to the internet through the Exchange 2007 with no problems. Can send mail from mailboxes on Exchange 2007 to internet and recieve no problems. CAN NOT send mail from mailboxes on Exchange 2007 to Exchange 2003 server. I have deleted and recreated the RGC and that did not help. The RGC is bidirectional. THe messages and public folders replicas just sit in the queue that is the full X.400 address with the error of "451 4.4.0 Primary target IP address responded with: 4.4.2 Connection dropped.Exchange 2003 server is running Windows Server 2003 SP2 and Exchange 2003 Enterprise SP2.Exchange 2007 Server is running Windows Server 2008 SP1 and Exchange 2007 Enterprise SP1 Rollup fix 5.There were no issues during the install.If anyone has any ideas of what may be a work around other than uninstalling Exchange 2007, I would love to hear.THanksSteve

Hi,Can you telnet the 2003 server from the 2007 server on port 25 and send a mail?Leif

Yes I can send no problems by telnet.

Have you run ExBPA at all? Weird permissions issues have caused mailfow issues like that, which ExBPA has highlighted before.Neil Hobson, Exchange MVP

Will it run on Server 2008? Or should I run it on my Exchange 2003 server?Thanks

Hi,It will run on exchange servers (installed on both on windows server 2003 and 2008)Leif

How is permissione set up on Exchange 2003 SMTP virtual server?Windows integrated must be enabled otherwise Exchange 2007 cannot authenticate to Exchange 2003 SMTP servicelarsp at avanade dot com, http://anewmessagehasarrived.blogspot.com

I have anonymous and Integrated turned on. Still can not get mail to flow back to Exchange03 from the 07 Server

The ExBPA found no errors on permission, but 2 of my 28 Domain Controllers are not at Windows Server 2003 SP2. But they are in different sites.

If this helps the only queues listed in the Queue Viewer areNext Hop Domain Delivery TypeStatusMessage Countcn=exchange03,cn=routing groups, cn-corbhub...SmtpRelayTo RgRetry189mercier-e2k7.levynet.com MapiDeliveryReady0Submission UndefinedReady0[192.168.1.202] Smarthostconnector... Ready0

How about name resolution? can the Exchange 2007 server resolve Exchange 2003 FQDN correct?larsp at avanade dot com, http://anewmessagehasarrived.blogspot.com

OK, I may have half solved my problem by looking at the FQDN. The SMTP Interface on my Ex03 server has a different IP address and is not bound in DNS to the same name. I created a new SMTP Virutal Server on my Ex03 server and gave it the IP of the server and the mail is now leaving the Ex07 and making it to the Ex03 server. But on the Ex03 server now the messages are stuff in the "Messages awaiting directory Lookup" queue. Any clues on why they would be stuck there now.

Nevermind that last one, a quick iisreset and all is well now. Thanks for the help. Our default SMTP server on our Ex03 server had a different IP address and was resolvable to the same name as the exchange server.ThanksSteve