What version of Go are you using (go version)?

$ go version
go version go1.20.1 linux/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

Fedora release 37 (Thirty Seven)

$ go env
GOARCH="amd64"
GOOS="linux"

What did you do?

https://go.dev/play/p/SWpZqP2Xxed

What did you expect to see?

An error.

Per RFC5322:

addr-spec       =   local-part "@" domain
local-part      =   dot-atom / quoted-string / obs-local-part
dot-atom        =   [CFWS] dot-atom-text [CFWS]
dot-atom-text   =   1*atext *("." 1*atext)
atext           = (Defined set of printable US-ASCII characters not including specials, see section 3.2.3)

So as I'm reading it the local-part is a single dot-atom-text (optionally with comments and folding whitespace around it but not inside it), dot-atom-text is a run of (atext or dot), and atext can only contain a defined set of printable ASCII characters.

Similarly, domain-literal doesn't seem to allow Unicode inside it either.

What did you see instead?

An invalid email address was parsed as valid.