1. I'll let you pass no questions asked:

* gotta have that '@' sign

* left of '@' sign must have greater than zero characters-- a-z, 0-9, dots are cool, plus whatever the rules are for international characters

* right of '@' whatever the rules are for domains

2. Pay me $1.99 through stripe to continue whatever you're trying to do, every time you're trying to do it:

* you've got double quotes, spaces, or other "actually, emails can contain..." bullshit in the local part of the addy

The errata are a doozy <https://www.rfc-editor.org/errata/rfc3696>, with a bad correction verified, a bad correction of that correction verified, and a reversion of the two incorrect corrections with incomplete justification (not quite mentioning the root cause, that you can’t actually use backslash-escaping outside a quoted-string like the RFC deliberately did) “held for document update” (which I suspect means that the reviewer finally realised the actual error, and decided it was too large to deal with with this way, but there are no verifier notes and I don’t know where the errata discussion records are, if they’re even public).

I wrote more, but it becomes all messy and confusing and I think I just discovered that according to RFC 2822’s and RFC 5322’s grammars, a space inside a quoted-string would actually need escaping, which would ruin "Fredd Bloggs"@example.com, which is widely understood to be valid. (This is because qtext lacks %d32 (space), which I think is accidental but it’s not entirely clear—it’s all bound up in the painful question of whether space is printable or not; see also <https://www.rfc-editor.org/errata/eid4692>. But their intent was clearly for space not to need escaping, as various examples all over the place use spaces unescaped in quoted-strings.)

So… I’m going to tip-toe gently away now and stop thinking about email address syntax for the rest of the day if I can help it.

/^\w+([\.-]?\w+)@\w+([\.-]?\w+)(\.\w{2,3})+$/