I find that being able to make folders to sort my messages is very helpful. Allowing premium members to do so might make it easier for players to keep track of which messages are about what. You could possibly restrict it to a certain number of folders (perhaps a max of 10) to limit it. For example:

Staff could sort their messages between staff messages and player messages as well as personal messages and any other things they might get.

Players could sort system messages from messages from other players or keep track of breeding offers/trade offers.

I think making it a premium feature would also be fair, considering that it's a specialized system.

Yes, that's a good idea. It would make cluttered inboxes look much more spiffy.

While i like the idea of having folders for our inboxes, i dont think it in itself should be a premium only feature as what happens to those folders if your premium runs out?

However, if we could have folders, maybe a bonus for premium members could be an option to auto sort messages, such as:

you have a folder named *game stuff* it would auto sort any messages coming direct from the game itself into that folder

you have a folder named *breeding* you could set it auto sort and messages with *breed/breeding/etc* in the title to go direct to that folder

this would then be a useful feature, but not one that would be *required*