email address checking wrong with hyphen in domain name

cannot use a domain name containing an "-" in the email address (falsely considered as a faulty character...). That should work...

For spam control I use a + sign in the local-part of the address.
On this forum that is not working also.

Is your issue with PWM to register, or with the forum itself?

Uhm, I remember wrongly.
The forum works with user+ovpn@example.com
It's PWM that does not accept it, https://community.openvpn.net/pwm/private/login