Maybe what we need is a narrower standard that subsets RFC5322 to remove (or at least deprecate) rarely used address syntaxes, such as double-quoted local parts.

(Actually RFC5322 already deprecates some syntaxes. For example, "John Hacker"."Ph.D., Esq."@example.com is a deprecated syntax (obs-local-part), because it contains multiple quoted-string components separated by dots.)

> or (brilliantly) two periods or underscors

Two or more consecutive periods is actually disallowed by RFC5322 (unless quoted). [email protected] is a valid address, [email protected] is not. ("foo..bar"@example.com is however)