Exchange 2003 FE & LTM

We do something similar to what you want to do. However our config is a bit more complicated but let me see if I can boil it down to something straight forward.

 

 

First let's talk SMTP. We are in the process of migrating from Notes to Exchange, so both environments are up and running. We have a VIP the load balances internal SMTP requests to our mail exchangers. Any internal application sending mail to ourdomain.com gets sent to a VIP defined by our internal MX DNS records. It is also the same VIP used as the default mail server by mail enabled applications (email.ourdomain.com). There is a pool of servers behind the VIP to process those requests. Outbound mail, from the environment is sent through another VIP to the DMZ based mail exchanges. Both VIPs round robin the load. The outbound VIP is protected and will only pass SMTP to the external exchanges for the internal exchanges, any other request is routed back through the internal mail exchanges for security reasons. Inbound mail works the same way only we first pass it through a spam filter first which is actually another VIP and pool. From there it's passed through the internal mail exchange servers.

 

 

Now for OWA. Internally, we use a VIP for the OWA environment. For external access, we do use ISA on the DMZ and then route to the same OWA VIP used internally. We use ISA for security reasons.

 

 

Hope that helps.