Example extension action

Here's an example extension action that raises an interesting question:

The action is called "denyMDN".  Based on: draft-ietf-receipt-mdn-06.txt

If the message has a "Disposition-Notification-To" header which matches
the envelope sender, then this will send an "automatic-ation",
"MDN-sent-automatically", "denied" MDN notification and remove the
"Disposition-Notification-To" header from the message.

The interesting question is: are Sieve scripts allowed to edit the headers
of a message?

                - Chris