hmm i think i have also seen that before i forget exactly what it was but the address was invalidly constructed as i recall (meaning it was not the proper format you’d expect to see for an email). i have noticed that wangguard’s server(s) are not always available (probably get attacked with some frequency). whenever wangguard is not online the plugin just lets people pass but it is rather odd that someone should even be able to complete registration without a valid email.
:/