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I was thinking about this aspect, and the first thing that popped into mind was the Hogwarts letters from Harry Potter. So imagine a mail-in game (I'll just call it a MIG?) where all the players are remote-learning "students" in an academy. All coursework and correspondence is handled through the mail for some as-of-yet undetermined plot reason. :P That setting gives you a lot of parallels to draw from for inspiration. (Grades for progress, assignments...)

Concept in progress, I'll post more after I've given it more thought. :)