I don't believe that "a@" and "a+tag@" being treated as the same address is part of any specification, but I could be mistaken about this. Many mail servers ha

I don't believe that "a@" and "a+tag@" being treated as the same address is part of any specification, but I could be mistaken about this. Many mail servers have a setting to configure which character to use; some default (or used to default?) to "-" instead of "+".