This came up during a support call, and the SmarterTools technician commented that he thought it should be a feature request. I'm not sure if he put that request in, but he did refund the support fee because he saw the need for this. SmarterMail's content filter will filter email between users, and it will filter email that is sent directly to the server. The content filter does not work at all on mail that is retrieved from an outside POP account. We have a few vendor supplied accounts that need the messages retrieved from them to be filtered into different subject folders based on the who and where, and the content filter does nothing. All POP retrieved email lands in the inbox or folder that has been specified for that account and cannot be filtered further.
I would love to see the content filter feature to be expanded to include mail that has arrived in the inbox via an outside POP account.