At our school we require all correspondence to go to the users official address. We prevent them from changing it in their profile, but with the new messaging system, they can set a custom address for messaging notices.
We would like a setting (in Site Admin>Plugins>Messaging Outputs>Email) or a permission, to set wether users can set a custom address there.
If there is a way to do this, would be glad to know. Otherwise, I'm starting work on a patch and will submit it here. We have to have it for our situation, so I'll be writing it regardless of it it's decided to be rolled in to Moodle.