I&#x27;ll try to avoid ranting here, but <i>anything</i> is a legal email address per the RFC (even an @ sign in a username, or an email address without any @ sign).<p>RFC 821 is the original and 2821 summarizes it plus the few that came after to add and clarify.<p>The only true &quot;RFC email validity check&quot; is to send an email to whatever address they provide.