We have a main office (with 50 mailbox enabled users and an Internet connection) and a remote office (with 5 mailbox enabled users and another Internet connection). There is also another connection between those offices just for "internal" traffic (AD, DNS, DHCP, VoIP, e-mail, TS, SMB...).
The main one centralizes AD Services, Corporate applications and files, Backup System and e-mail. In fact, there is just an Exchange Server 2003 server in that office that manages all incoming and outgoing messages of the company.
All three WAN connections are ADSL and we created a VPN for interoffice communication.
The problem appears when we want to optimize the traffic between those offices, mainly for Active Directory and Exchange Services.
We thought to create two separate sites, one for every office, with their own DC, DNS, DHCP and Global Catalog, synchronizing data on an scheduled time. Related to e-mail routing, we thought on installing another Exchange 2003 Server on the remote office, just for allocating mailboxes for those 5 users. In the final scenario, all incoming SMTP traffic would arrive to the main office and then stored there by default, unless for those 5 users, whose e-mail would be "routed" to the new Exchange Server (how does it works? is it needed to create a connector on the main Exchange Server?). And outgoing mail would be delivered for every office through its own Internet Connection.
In order to prevent to match antispam filters (based on DNS records A, MX, reverse DNS, Hostname FQDN, etc.) we would configure a host and MX (with higher value) record for the remote office Internet connection and the FQDN of that Exchange Server. To prevent using the new MX record, we would also deny on the remote office's router incoming SMTP traffic.
Do you believe this is a good solution for optimizing traffic (e-mail and domain services) between offices?
On the Exchange traffic, which action or item needs more bandwith?
Related to the Backup:
How could we centralize the daily backup job of the mailbox storage? Would it be necessary to send (through the interoffice WAN connection) all the 5 users mailbox data in a full backup? Is there a faster way different from using differential or incremental copy?
Would it be possible to create all the mailboxes in the main office Exchange Server and just a copy of the 5 remote users mailbox in the remote Exchange Server? And synchronize just changes on the 5 mailboxes on a scheduled time?
I will really appreciate your help, ideas or suggestions.
Thanks in advance.