Scrubbing text from outgoing messages

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Does anyone have any experience with removing certain text strings from what is displayed in the system generated emails?  We have text that shows up automatically on all incoming (if its from an external domain) and outgoing messages.  Since all of our tech mail is routed through our mail domain, both ways, we are seeing both text strings in the email response.  Is there a way using rules to suppress certain text?  I've played around with conditional and case statements in the message templates but haven't found a way to remove text based on the condition.  Attached is an example of the outgoing disclaimer and the incoming alert that our customers will see in the Question Receipt email when they submit an incident.  We are in the process of testing the migration of message templates and set to deploy prior to our upcoming upgrade.  Would be nice if the unnecessary stuff can be scrubbed.