whats the best setup method for the following scenario,
i have 4 sites of which one i have designated my main site and of which i would like to install a new exchange sever possibly clustered on this site only i dont really want to install a exchange server in each site if i can help it. thing i have wan links between all sites and ad configured and working but my wan links are very busy all day and i dont really want to put any extra traffic on the wan links. i also have vpn links between the sites just for backup really. would it be possible for me to force all the email traffic that comes into my main site on the ad back out through the vpn links for delivery to the branch sites if neccessasry and similarly if a user at the branch office sends an email i dont want it coming down my wan link to goto the exhange server at the main site to got out rather either go straight out to the net or again come down the vpn tunnel instead to got out.