<i>&gt; I think this is actually a feature in many different products from different vendors.</i><p>It is, but it sounds badly implemented as described here.<p>Stripping headers and sending on the rest of the message with no care for the content is bad design, you are essentially corrupting a request or response.<p>If there is a problem with a message discard or quarantine the whole thing and log the event (in the case of SMTP perhaps send the target a &quot;we blocked this, check with the sender if you really need it&quot; and&#x2F;or the sender a bounce if you are reasonably sure the sources headers aren&#x27;t faked) for future analysis.