Well I have the email, and the offer is for Advance Singles for travel between Oxford and Paddington between 11th Jan and 2nd March from ^6.
Given that I live in Didcot and don't fancy travelling to Oxford to get a cheap ticket it isn't of much use.
Maybe I was sent the email because I live in an OX postcode
Although I don't really understand why you can't purchase advance tickets, towards London, from Didcot, given that I believe that you can purchase them on all the trains that go through Didcot towards London e.g. Cheltenham, Bristol, Oxford, Worcester etc.