You should always treat that case as distinct email addresses. If you have problems with one person signing up multiple times then this won't fix it for you. T

You should always treat that case as distinct email addresses. If you have problems with one person signing up multiple times then this won't fix it for you. There are many other ways a person can have lots of email addresses. You will waste a lot of time chasing your tail. I reasonably use plus style addresses to establish different identities and I generally pass on a website if their registration or other processes assumes things about my address or disallow valid characters in an email address. I also don't try and rip-off a website by abusing their free services.