Smart Host problem - 3x Back end servers, no FE server

We have three back-end Exchange 2003 servers, all SP2. There is no front-end server.

Two are in one site - we'll call those London1 and London2. The other is at a remote site, we'll call that Remote1.

Up until today, London2 and Remote1 have London1 configured as a Smarthost. This then send's e-mail using DNS lookup. Today we setup with a 3rd party mail filter, Messagelabs. I configured London1 to relay all e-mail via Messagelabs (I.e. I configured messagelabs as a smarthost under the smtp virtual server on London1).

Since adding the smarthost, some of the e-mails sent from mailboxes on London1 to mailboxes on the other servers end up in a queue called remote1.ourdomain.com and london2.ourdomain.com and then move quite quickly (couple of minutes) to the 'Messages queued for deferred delivery' queue.

If I take the smarthost out of London1, mail flows around the company fine.

I want to use the smarthost for all mail that leaves the organisation but I also want mail to flow properly between my back-end servers. I think the solution might lie in routing groups and connectors but I'm not really sure what I'm doing with those.
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tlcsupportAsked:
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aa230002Commented:
How many Routing groups you have and how these servers belong to these routing groups?
You dont need to give smart host on all servers our your organization. You just need to define routing groups and then create routing group connectors between them for mail flow.

On London1 server, i would recommend you to create a SMTP connector with Address Space * and then send all mails to 1 single IP of MessageLabs using this SMTP connector rather than giving the smart host on SMTP virtual server properties.
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tlcsupportAuthor Commented:
All 4 servers are in a single routing group. Perhaps this is the problem.

If I create a connector with the address space of *, internal e-mail destined for the other servers attempts to go out via the connector.
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tlcsupportAuthor Commented:
Having removed Sophos Puremessage, the problem resolved. Very strange behaviour. We've since replaced the offending Exchange server and installed Puremessage onto it and do not experience the same problems.
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