By all means, validate. But err on the permissive side. The odds are pretty great that you're wrong, and you're preventing real email addresses (and almost certainly real users) by doing so.

I'd never looked closely at Django's email validation, but after looking at it I'm inclined to stop using it. Example reason:

> # max length for domain name labels is 63 characters per RFC 1034

There is a high likelihood that most of your users have shorter domain names, and also a high likelihood that most if not all registrars currently enforce this. But it also used to be highly likely that domains didn't begin with a numeral, and even though it was disallowed, 3m.com existed.

Another: neither the tests nor the patterns account for unicode, which is valid for domain names irrespective of the local part, and if not allowed for the local part by existing providers almost certainly will be eventually.

Also, a thing I noticed in the Django tests that is just upsetting:

- name: `TEST_DATA`

- values: `(validator, value, expected)` (a validator of the data is not the data)

- unstructured groups of such that should almost certainly be structured