As very little of my recipients use encryption, I normally do remember to turn on encryption for them. But sometimes I forget. Encryption always preselected is much more of a problem.
So I'd like an algorithm that checks if all recipients' keys are known and automatically turns on/offers encryption. And turns it off again if the recipients are changed to non-key ones.
If this is too difficult, I'd like an algorithm that checks just the first recipient once and turns on/offers encryption if that recipient's key is known. This would work in 99% of my cases. I guess this makes my request new if I missed an old request for the same thing.