Letter through time

Forgot to link paste, excuse me.

Basically:

>In the woods, there lives a mage in a camp that studies timetravel magic
>A young Earth Pony arrives per train to bring him a letter
>He has a sprained leg though, and tells PCs to deliver the letter
>PCs run into an NPC 4C mailmen, spilling letters everywhere by mistake
>Accidentally pick up wrong letter
>Deliver letter
>Letter was "ur a fgt"
>Mage sends letter back in time
>Goats find it, build tower to house it