Thank you both for your work on this.  The patch I committed is a combination of my _addr_only, Filipe's tests, and Catalin's modifications to those tests.  quoteaddr, although in the __all__, is not documented and is really an implementation detail, as is the new _addr_only.  So I am only testing them indirectly through the documented parts of the API (I added a test for <> address, and one for an IDNA encoded address).

Catalin, I think you are correct about the try/except/None stuff.  As far as I can tell it is left over from the old days before the email package and its philosophy of never throwing parsing errors.  Nowadays if parseaddr throws an error, it is a bug.  That's a refactoring not a bug fix, though, so I didn't backport it.