> it's just a comment that will be ignored. It’s not a comment. Some mail services allow you to have aliases in the form of normal-username+something@service.c

> it's just a comment that will be ignored. It’s not a comment. Some mail services allow you to have aliases in the form of normal-username+something@service.com but that doesn’t mean all do. If it were a comment the address +@example.com would be invalid but it’s not. Comments in email addresses are written in parentheses like username(i'm_a_comment)@example.com.