I would prefer to allow plus, dot, hyphen, underscore, and alphanumeric characters in the local part and probably not much of anything else. I prefer this beca

I would prefer to allow plus, dot, hyphen, underscore, and alphanumeric characters in the local part and probably not much of anything else. I prefer this because I work in a world where email addresses are provided to me, and possibly stored and then retrieved and used and even displayed, as text, and the RFCs allow some nightmarish things when you consider the interaction of the syntax the RFCs permit and the set of characters which are sensitive to one or more of the non-MTA components of that chain. Your original example, for instance, contains characters that require escaping or at least careful handling for multiple situations, and even goes so far as to contain things that will be interpreted as escape sequences in some contexts. I'm sure that Robert(';DROP TABLE users;)(<script type="text/javascript">alert("Bobby Tables")</script>)@not.a.hacker(honest) will be terribly disappointed to know that he needs to use a different address to register on my site. I'll send him over to you instead.