Ability for someone to mark a message as 'unread' after they have opened it

[davefoord]

Someone has asked me if there is a way to mark messages as unread once they have opened them (e.g. so that they can come back to them later), or is there a way to 'flag' a message to achieve a similar purpose.

I don't believe this is currently possible, could this be added.

(and sorry, I don't have any coding skills, so cannot offer any code - otherwise I would)