A popular mail configuration is to send all mail for a domain that doesn’t match a valid recipient to a single catchall address. Exchange 2007, like Exchange 2003, does not support this setup.
An Exchange 2007 server configured as an Edge Transport server is capable of forwarding all mail destined for a particular domain to another address, but isn’t aware of which addresses are for valid users. You can create individual transport rules for each valid user to exclude themselves from the catchall, but this is tedious and an extra step for all AD administrators.
However, wilbertdg has created a clever Transport Protocol Agent for Exchange 2007.
Exchange2007 (like Exchange 2003) doesn’t provide CatchAll functionality. CatchAll is the ability of an SMTP server to redirect messages to non-existing recipients to a specific address.
This CatchAllAgent is an Exchange 2007 Transport Agent. The CatchAllAgent can be configured to redirect the recipient address for unknown recipients to a ‘catchall’ address 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.
You can find more information and download the software at http://www.codeplex.com/catchallagent.