A. With Exchange 2007, you can deploy multiple Hub Transport servers within a single Active Directory (AD) site to provide mail flow redundancy and load balancing. However, if the Hub Transport server crashes, any mail still in its queue is lost. There’s no disaster recovery for the Hub Transport server role queue. You could create multiple Hub Transport servers in a location, but they wouldn't replicate queue content.

The only viable option I've found is to replicate the transport queue content or place the queue on an external storage device, such as a SAN. If the Hub Transport server crashes, the queue and transaction logs (the mail.que, trn.chk, and .trn files) can be moved from the storage device to another Hub Transport server and processed using the instructions at Working with the Queue Database on Transport Servers. Then you would use the Eseutil /r Trn /d. /8 command in the new Hub Transport server folder to read the files into the new server for processing.