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Share and sync calendar data between two Exchange Server sites

Find out how to set up trusts between two Exchange Server 2003 sites to share and synchronize calendar information between users.

We have two Exchange servers (Exchange Server 2003 SP1) operating within a group of companies on two separate sites and Active Directory (AD) infrastructures. There are currently no trusts between the sites, but we have a common link between us. The business now requires us to be able to book calendar appointments and tasks between users on the separate Exchange servers. IT would also like to utilize this for disaster recovery and failover between sites. Is this possible without some form of trust between Exchange Server sites? If not, what would be the best solution?
No, it's not a possibility without setting up trusts between the two Exchange Server sites. If you already have a secure link, like a virtual private network (VPN) tunnel created between the two sites, I don't see why creating trusts should be a problem to meet business requirements.

Once you create trusts, you can use Microsoft Identity Integration Server (MIIS) Feature Pack 1a's GALSync tool to synchronize global address lists (GALs). This allows recipients from one organization to be replicated as contacts in the other organization and vice versa.

The next step is to use the InterOrg Replication Tool to replicate Free/Busy information. This allows recipients from one organization to schedule meetings with recipients in the other organization, and to be able to view each other's free/busy information.

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