A common issue I've seen is websites treating a period in email addresses differently. All discussion about standards aside, the fact is * To Gmail, firstname.

A common issue I've seen is websites treating a period in email addresses differently. All discussion about standards aside, the fact is * To Gmail, firstname.lastname@gmail.com and firstnamelastname@gmail.com are the same. * To a website like Paypal, they are different. So it will allow multiple signups with the 'same' email address. I just had to troubleshoot this for my parents, who have separate Paypal accounts, but tied to the same email account.