Sorry if this has been asked before - I searched 'email address' and 'e-mail address' without finding a similar query.

My wife and I are both HHonors Diamond, with separate HHonors accounts. However both for convenience and my superior knowledge of all things HHonors related () I handle all our hotel reservations. If I try and add the e-mail address registered to my account to my wife's account I get the message - 'Sorry, that email address is already registered. Enter a different one and try again'.

Is there something in US law that explains this issue? By way of comparison I have a British Airways Executive Club household account with seven family members - I am able to use the same e-mail address for all seven individual accounts: it makes life a lot easier when coordinating reservations.