I need to get Postfix to inspect the MAIL FROM of the envelope and determine whether it matches the authenticated user of the session. If it does not, it should then add or update the "Sender: " header inside the e-mail so that its value is that of the authenticated user. I understand that this can be done using sender_canonical_maps but, having tried a few remedial tests, I'm unable to get it working. More than anything I would like to know whether this is actually possible with Postfix, and secondly whether I am in the right ball park. Lastly, an example of how to do it would be fantastic. Thanks very much.