Connecting Exchange Servers Across the Internet

Our main Exchange 2003 server is at a hosting provider.  We have a site-to-site VPN connection to them but we always access the mail server through the Internet, not the VPN.  I recently added an Exchange 2003 backend server plus an Exchange 2003 frontend server at our local office in preparation to move all email locally.  This would be a gradual transition where mailboxes would be moved over a few at a time. I've done testing on this setup and all servers can communicate with each other fine through the VPN; all mail is delivered to the appropriate mailboxes.  I moved my mailbox to the new local server and used the new frontend server for a week without incident.  When I went live with this new configuration, I made the change in internal and external DNS to point all users to the new frontend server.  Things were fine for a day or two but then the VPN hardware on our side became nonresponsive.  Turns out it could not handle the load.

My question is is there a way for the local and hosted Exchange servers to communicate with each other over the Internet instead of the VPN route?   Every search I've done on this topic involves using a VPN connection.  I'm looking for a definite yes or no on whether this can be done, and if it can what are the steps to do it.
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you mean you still have most of the user on host and some on local, right?

Then why can't you change the DNS to the way it was?? since you have less user on your local.  So when  the user that reside on the HOST connect it will connect directly with HOST. but when you want  to connect to your mailbox it will first contact the HOST server first then the HOST server will forward the request to your FE server.  This way the VPN traffic should be minimal.  

Also, Check your VPN configuration.  It should not matter where the user connected to. Either HOST or FE server. there should be only 1 tunnel open between your server and HOST.

to link both exchange over internet, I think it is possible but you will have to open lot of ports. which is increase security risk for your server too.

port use by exchange need to open,289483,sid43_gci1124126,00.html

NyactonAuthor Commented:
Thanks for the response.  Right now, all live accounts are on the hosted Exchange.  I have a test account on the local.  DNS is back to the way it was.  If I connect to OWA, which is pointing back to the hosted server, with an account that has a mailbox on the local server, it's going to fail.  That's why I need the front end server...I don't want to have to have multiple OWA addresses or manually configure email clients.  As for the VPN, there is only one tunnel.  The device itself becomes nonresponsive after a while (can't ping or get to web interface) but machines on the other side are still accessible but intermittently.
I don't think HOST server willing to connect to your site. How many users are you talking about??

The problem is you can't move few users at a time. because your domain MX record is point to HOST server not your Front End (FE).  If you do move some user over to your server, those users will not get new email unless you forward them  but you can't forward to your own domain.

Ask your HOST if they can provide PST file for all of your users.(they can use Exmerge), If they can. Then you create all users Email box on your BE server.
Notify your user of downtime.
Change MX record from you domain registrar to point to your FE instead of HOST (allow up to 24 hrs for worldwide change)
Change your Internal DNS to modify OWA address to point to your BE server
Change your External DNS to modify OWA address to your FE server IP
 Copy PST file to your BE server.
Then Exmerge PST into your BE server.

This way you user will use the same address.  when user connect locally, they will connect using LAN.
when they connect from home. They will connect to FE and FE will connect them to the right server.

If you currently connect OWA via internet right now. what is the purpose of the VPN site-to-site then??

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NyactonAuthor Commented:
Everything I've been reading says it's bad news to open the Exchange servers to the Internet which is my original question.  Thanks for the help.
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