This problem has NOT been solved in general.
The validation of the e-mail address in the registration form (
https://community.openvpn.net/pwm/public/newuser) is buggy. It doesn't accept a minus (-) beeing a part of the domain name. Same with an underscore (_) in the local part. Both are allowed according to RFC 5322 (
https://tools.ietf.org/html/rfc5322#section-3.4).
Tested a few minutes ago with Chromium and Firefox.