Lets say, just out of curiosity, that someone in early december were to dump all their minerals into a gate, and then not play for about 6 weeks.
When they come back, should they expect to see their messages with heat and crowns still there, waiting for them, or do they time-out after a while?
Well I didn't play for a while and my messages were still there, so I imagine they just accumulate until a gate goes away and sit there until you claim the reward.