Cancust,

To better understand your network structure, can you offer some additional information about what type of mailing platform you are using. Is this an exchange environment?

Since i can only assume you are working with exchange, these users should all be in your GAL if they are within your exchange network.

When constructing the rule, there are not a lot of choices when a message arrives from a specific person or group. To move an incoming message based off the second address is not an option even in Outlook 2010.

Several attempts to replicate and per pose a work around or a solid solution doesn't seem likely. Several tests indicated the address the delegate is sending on behalf of will not trigger the rule if the rule uses that second address. This was even done with both addresses and only the first address would trigger the rule.

Hope this helps