I just referred to a separate email address (in my case it is 100% legit - I run my own business as a contract worker, so I have personal and professional emails). I don't think they really cared though. When my business referred me, I used the link but stated I did not have a current AMEX account - I thought I had cancelled my SPG card several months prior, turns out that had not actually been carried out properly, so my new card has a "member since 2009" on it. (Which is what prompted me to check into the cancellation of the SPG card!)