It was pointed out in the comments that hadn't appeared on here - which given the letter was issued a good few weeks ago I thought unusual - and voilla!
I think it's a fake. and OMAAT went for an exagerated headline leaving the 'alledged' nature of this letter to a sentence below.
I don't think anyone at DL would have sent such a badly worded letter and if they did wouldn't it be easy for DL to find out who had accessed his account?