Sorry, this fell out of my head for a few days.

It was a ~1000-person national level game in a fantasyish setting, and one of the game elements was that you were explorers and colonists in a strange new land, and you could send messages to your supporting factions "back home" to request support or supplies or whatever. Those messages had to be carried by a ship belonging to a trade house, and any supplies that your supporters sent you had to come back by the same method, and all the trade houses were represented by player groups on the field...

So yeah, a group of players would write to their "sponsors", and my group (as one of the trade houses) would open their letter, see what they were requesting and then forward the letter to the game organisers. The organisers would play the part of the remote sponsor, and send a letter back, which we'd open and read to see what orders the players were being given and what support they could expect (then we'd reseal the letter and deliver it). This positioned us super well to sell them exactly what they needed to achieve those goals, at an only slightly elevated "rush" price.

We didn't open every letter, and we didn't scam everyone - we made most of our money legitimately. But it was a fun side-game.