In Microsoft Entourage, you will sometimes run e-mail scripts on received messages. You may have noticed that you can enable Entourage Rules (on the Tools menu) to run automatically on messages as they come into the Inbox. One possible action that the rules can perform is to Run AppleScript. Similarly, Schedules (also on the Tools menu) can be set to perform tasks either on a regular repeated schedule, at startup, or on quitting, and can also Run AppleScript. Both of these provide a high degree of customization and automation, since AppleScript can do almost anything with Entourage objects, far more than standard rule and schedule actions can do, and with a finer degree of selection and combination.

You may be frustrated with rules that let you filter when "all criteria are met" (that is, boolean and for all conditions) or when "any criteria are met" (that is, boolean or for all conditions), but you can't filter for finer or more complex granularity. AppleScript can handle any degree of complexity, so just write it as a script and run the script from the rule.