Answer:
by Randy Carey:
You would need a power of attorney or you might be joining your friend soon.
Answer:
by John Burnett:
It's possible, though doubtful, that your friend's letter from "inside" giving you permission to cash the check would meet minimal requirements for a limited power of attorney in your state. I'm certainly not in a position to say that it is or isn't; a lawyer in your state might tell you. But even if it met the bare letter of the law in your state, I think most banks would not accept it as valid, and would refuse to cash the check.