You haven't come up with a single reason why it can't be the Greybeards besides reasons like 'They can't find a courier!' when they're the same people that summon a thunderstorm and call you out from the SKY.Meanwhile your best theory is a stalker named Arnold with no motives other than lulz. They're also not upfront at all in the beginning. And they already tell you where Words are without any retarded waiting and doesn't make sense they will do this two ways. A bit more probable, but they don't really leave their mountain so I don't see how they would know when you shouted, Then again they heard you when you first killed the dragon, but still don't have access to a courier. I know where a bunch of Words of Powers are, but instead of telling you, I'm going to wait until you shout somewhere, then have a courier hand it off to you in the form of an anonymous letter. I guess it could be the guy at the bar handing off the letters, but doesn't really explain the whole 'Hey. Also, you can get these letters before you meet Delphine, yet Delphine had to get the horn before you did to find out who was the so called Dragonborn. Of course there is a chance Delphine could of hid in robes to hide her gender. The courier says something along the lines of ' He only said he was a friend'.
