troubleshooting Question

Exchange 2003-2010 Co-existence - no mail flow from 2003BE to 2003FE if no smarthost

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Hans KristiansenFlag for Denmark asked on
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Assistance needed for implementing Exchange 2003 – 2010 co-exeistence; How to set up Exchange 2003 Backend server to send outgoing Internet mails through Exchange 2003 Front End server without using Smarthost.

We are in the middle of performing a migration from Exchange 2003 to 2010. So far, we have installed two new Exchange 2010 servers (one for Edge and the other for the rest of the roles) and imported a new SAN certificate on the Cas/Hub/Mailbox server.

For purposes of this discussion, I will name our relevant servers as follows:
2003BE (2003 Back end server, where the mailboxes are located) – this is on LAN
2003FE (2003 Front End server) – this is in the DMZ
2010CHM (2010 Cas/Hub/Mailbox) – on the LAN
2010Edge (2010 Edge) – in the DMZ

We are now attempting to implement a ”co-existence” stage, and noticed that we only have one-way communication from the 2010CHM to the 2003BE server (and no communication the other way).

According to multiple articles, this is usually caused by a “Smart Host” having been configured on the Virtual SMTP Server on 2003BE. And sure enough, that’s what we have on ours: Back in the beginning of time, somebody put a Smarthost entry there – and this entry points to the 2003FE server. This apparently causes mails that are supposed to go from 2003BE to 2010CHM to instead get directed to the 2003FE server, where they queue up (in a “deferred” queue – and they never get delivered to 2010CHM).

If I remove that Smarthost entry, I do indeed accomplish having mail flow from 2003BE to 2010CHM, so in that regard the “remove the smarthost entry” solution works.

However, the big problem then is this: Without that Smarthost entry, outgoing mails to the Internet start queuing up on 2003BE and do not get delivered.

As far as I know, mail flow to the Internet is supposed to be able to proceed from 2003BE to 2003FE without any smarthost entry, but clearly this is not the case in our setup.

Can anybody help by telling me how I can get Internet mail to flow from 2003BE to 2003FE without a smart host entry? Or by any other insights that may help us get this co-existence running?

I have, among other things, attempted to solve the situation by keeping the Smarthost entry on 2003BE and instead creating a “RoutingGroupConnector” between 2010CHM and 2003FE, but no go – the mails destined for 2010CHM still get cued up in a “deferred” queue on the 2003FE server (which, FYI, does NOT have a Smarthost entry).

Thanks in advance for any attention :)
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