unknown email

hi, i have an 4s and my son tryed to use it so he started with the activation, and he locked it with find my iphone, the matter is that he forgot what email he used and without it i cant access or activate the iphone, his name is gregory and the account used start wit g........@hotmail.com i tryed many emails and nothing, so i want to know if possible wich email he used, so i can release the phone. thanks for help