That's probably it: a simple boolean header. And I agree that changing default behavior is a very dodgy practice.
I used to have an Outlook extension that disabled Reply-All on outgoing mail. I used the heck outta that thing! Nothing bugged me more than someone sending an e-mail broadcast to the division, which would be followed in my inbox by a dozen or more Out-of-office autoresponders.
I used to have an Outlook extension that disabled Reply-All on outgoing mail. I used the heck outta that thing! Nothing bugged me more than someone sending an e-mail broadcast to the division, which would be followed in my inbox by a dozen or more Out-of-office autoresponders.