CatchAllAgent is an Exchange 2007 Transport Protocol Agent. If a message comes in, and a
recipient of that message does not exist (unknown recipient), the recipient typically gets
rejected by the Recipient Filtering feature (which is also a Transport Protocol Agent).
The CatchAllAgent can be configured to rewrite the recipient address for unknown recipients
such that such messages end up in a dedicated mailbox. The configuration allows for multiple
domains, but you can only specify a single target address for each of those domains.
Read the complete guide here -> http://www.petri.co.il/setting-up-a-catchall-mailbox-in-exchange-2007.htm
Thanks to Wilbert De Graaf for creating the agent.