Fernpost
FernpostFernpostWeb
Schedule your newsletter and forget about it.
Someone unsubscribed on the Tuesday, got the confirmation page, and received Thursday's issue anyway. She emailed me about it rather than you, which is the part I mind.
I've checked her record and she is definitely marked as unsubscribed. My guess is the queue was already built before she left.
You've diagnosed it correctly, and this is the worst thing on the board so I'm treating it that way.
The queue takes a copy of the recipient list when the issue is scheduled rather than when it sends, so anyone who leaves in between is still on the copy. Somebody asking to be left alone and then being written to anyway isn't a rendering problem.
Half of it is out now. The send re-checks against unsubscribes in the last moment before it goes, so the window is seconds rather than days.
The half I'm still writing is an audit line on each subscriber, showing when they left and what went to them afterwards. Without it you have to take my word for this, and after what happened you shouldn't have to.