What does message tracking, or mail_logs reflect for the message? Where is the disclaimer stamped at - is it configured in message/content filter, or is this stamped in at the listener level? You should be seeing "add-footer filter 'Footer Stamping'" in mail_logs...
If it was for just one email - I would have to think that there was something else that stripped out the disclaimer - at recipient end?
If message tracking/mail_logs shows it placed - then the ESA wrote it in as configured - would need to validate at some other point in the message delivery to show what might have occurred.
Hope this helps!
-Robert
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