> So just...don't send it? I don't see why having done prior work to compose it means that you have to send it. So just heavily modify sendmail/qmail/whatever

> So just...don't send it? I don't see why having done prior work to compose it means that you have to send it. So just heavily modify sendmail/qmail/whatever to maintain a list of email addresses for which it shouldn't send it? Not associated with the grandparent, but the software likely composes and immediately "sends" the email, at which point it's going to be in MTA queue that's completely oblivious to the fact some email addresses have been unsubscribed since they entered the queue. Overall, what you're suggesting sounds somewhat unreasonable. Once the email is "sent" (actually, added to MTA queue!), he might have no control whatsoever what the MTA does. If you throw a stone, stopping it mid-air can be... hard. Perhaps it's doable. But is it a reasonable expectation?