I think it's simply a hybrid approach: you'd handle those unknown contacts with many:1 addresses (since there's no real alternative, as you imply), and you'd ha

I think it's simply a hybrid approach: you'd handle those unknown contacts with many:1 addresses (since there's no real alternative, as you imply), and you'd handle most known contacts with 1:1 addresses. A benefit is that you might let messages to some or all of those 1:1 addresses be sorted one way (e.g., they ping you) while messages to some or all of the many:1 addresses are sorted another way (e.g., you only check for them with a much longer interval). But then again, a diligently-maintained contact list can be leveraged to achieve same...