I think what I want to do is quite straightforward but I can't see the how to implement it.
We have some emails coming in to our exchange server from an external source that are duplicates of messages we already have, these are generated from a server outside our control so we can't stop them but they all have INTERNAL at the start of the subject line.
Quite simply what I want to do is get exchange to not delivery / delete any messages where the subject line starts INTERNAL but not any message that contain INTERNAL. So for example 'INTERNAL abc' would be deleted but 're: INTERNAL abc' wouldn't.
I thought I could implement this as a hub transport rule but I can only get that to work when the whole subject line matches, how do I enter INTERNAL followed by a wildcard?