I introduced my first EX2010 server in my single server EX2007 environment today. All is working except for mail being sent from a 2010mailboxto a 2007 mailbox. Messages simply sit in the queue on the 2010 server.Iheard this issue is because of the new version routing and incompatibilitywith EX2007 and 2010 HT servers. Is this true?If so,how is one expected to do a swing migration?Thanks!

Do you have a 2010 HT as well as a 2007 HT? This is necessary.See here: Upgrading from Exchange 2007 Transport http://technet.microsoft.com/en-us/library/dd346708(EXCHG.140).aspx

Yes, my EX 2007 HT is still online

Are all 2/4 servers:2007 MB2007 HT2010 MB2010 HTin the same AD site?

Yes they are.. I only have one site in AD

I checked my Default Receive Connector on the 2007 HT. The connector is configured to accept connections from Exchange servers. I also checked the time and they are within one minute of each other. Its weird, I can send mail from 2007 > 2010 without issue. I can also send and receive externally on 2010. The only thing not working is mail sent from 2010 > 2007.

When 2010 sends to 2007 it uses versioned routing. Sounds like the issue may be related to this.See here: To enable message flow across versions, a feature called versioned routing is implemented in Exchange 2010. With versioned routing, the routing engine checks the version of a mailbox's home server, along with its Active Directory site. If the version does not match, then the message is relayed to a Hub server that has a matching version (see versioned routing workflow in Figure 5). In effect, routing is now dependent on both Active Directory sites and Exchange versions. Figure 5 Versioned Routing Workflow When an Exchange 2010 mailbox user sends a message to an Exchange 2007 mailbox user in the same site the following occurs: The Exchange 2010 Mailbox server notifies the Exchange 2010 Hub server of the new mail. Exchange 2010 Hub picks up the message. Routing agent determines that the version of the Mailbox server that is the home server of the destination mailbox does not match its own version. Routing agent locates an Exchange 2007 Hub server in the local site. Exchange 2010 Hub server relays the message to the Exchange 2007 Hub server. The routing agent on the Exchange 2007 Hub server determines that the target mailbox is on an Exchange 2007 Mailbox server in the local site. Exchange 2007 Hub server delivers the message to the Exchange 2007 Mailbox server.

Your Exchange 2007 server(s) has SP2, right?What is the NDR users are getting and/or the error listed in the queue?

Yes I am running SP2 "Version 8.2 (Build 176.2)"My HT queue version are as follows: 2007: smtp.comcast.net (my smarthost)2010:hub version 8 (my test messages from 2010 reside here)So to my knowledge 2010 should see that the target mailbox in on 07 and forward accordingly.

And to confirm, no special connector needs to be created right? I assume internal routing between HTs is based on AD sites.

You do not need to make any connector for Exchange 2010 and 2007 to communicate. Your messages that aren't getting delivered from 2010 --> 2007; what is the error message here?

I justnoticed the following in the queue viewer on 2010:451 4.4.0 DNS Query FailedI am reviewing my internal split DNS now

yes, that is what i was asking about. Perhaps clear out your smart hosts and verify it works without them, and then put them back after you've verified DNS.

Ok.. all is well now. Here is what I did. - Unchecked IPv6 and removed my router as the secondary DNS server on 2010- Deleted my internal split DNS zone (I must have created it months ago and forgot about it)- Cleared cache on DC and restarted DNS Server Service- Restarted transport service on 2010I am still confused as to why this worked... I wonder if adding a MX record to my internal split DNS zone would have resolved?Thanks for sticking with me!

Yeah it seems the split DNS was likely the cause. perhaps it couldnt find a necessary record for the DC or another server.

In a similar scenario, where Exchange 2010 Hub could not send to Exchange 2007 Hub (while the opposite was working correctly), I created a new Receive Connector on Exchange 2007 with the following attributes: Network: Receive mail from a specific IP of Exchange 2010 Hub Authentication: TLS, Exchange Server Authentication Permission Groups: Exchange Servers After this, mail flow was restored.