A strange little problem has happened, and I would like some help. We have just started to deploy Exchange 2007 in our organisation. We have 2 Exchange 2003 servers ("ServerMX1" and "ServerMX2"), and have deployed our first Exchange 2007 server that is Hub Transport and CAS. This works well, all email to and from our organisation goes through Exchange 2007 on this server "ServerMX5". We built our first Mailbox server (Win2008), and installed Exchange 2007 SP1 Standard Edition. This was then tested as working fine, a test mailbox was migrated to it and mail flowed to and from the new mailbox server "ServerMX3". We then realised that we needed 2007Enterprise Edition, so uninstalled Standard Edition, rebooted and re-installed Enterprise Edition [we have realised now that we didn't need to do this]. We have also installed Update Rollup 4. "ServerMX3" is our new 2007 Mailbox server, and we have moved a mailbox on to it, and are able to send email from "ServerMX3"(2007) to "ServerMX2"(2003). But, we cannot send email from "ServerMX2"(2003) to "ServerMX3"(2007) - the queue on "ServerMX5"(2007) states the error message "There is currently no route to the mailbox database". Any ideas? Where can I start looking? Mail from Exchange 2007 to Exchange 2003 flows Mail through Exchange 2007 HTto and from the Internet flows Mail from Exchange 2003 to Exchange 2007 flow - but only to the HT server and not then on to the MBX server

Hi Chris, Get-RoutingGroupConnector | FL can give you more idea about the routing groups configuration between 2003-2007.

A reboot of the HT server resolved the problem.