Ability to pin certain DM threads to the top of our messages page

Some us MDL users use messages quite a lot with various users. It would be helpful to be able to pin a certain amount of threads to the top in our inbox so that we can find them easily.

Whether it be threads with info we want to reference back to, a conversation we want to follow-up on, or just a message thread with a user we talk to a lot and don't want to get buried in times of inactivity.