I've got the same letter from... uuuum... dunno the name. that guy that runs the farm just outside of Whiterun (the one next to the stables).
Strange thing is: I've just talked once to him, sold him all my potatos and cabbage and ever since he greeted me with a warm "It's good to have someone like you around!"...
one time I left Whiterun, went down to the stables to gather my horse and be I saw a dragon circling around that farm and engaged him in combat...
the farmer dude (that imperial guy with the reddish-brown garment) died during the attack and a few ingame days later (I wasn't even thinking of the incident anymore) a boy arrived and passed me that letter of inheritance with 100 gold attached.