Comment by seadan83

Not all mail servers treat a+b@a.com and a@a.com as the same email.

By equal token, you can't be sure that the email address doesn't actually just contain a plus sign.

I was disappointed to find out at work recently that the plus convention was not configured. It made testing account signups more difficult. This is when I dug in a bit and found it that it depends in the mail server for whether those are unique addresses or not.