@Override
    public boolean isEmailRequired()
    {
        // If at least one provider does not require an email, neither is this proxy.
        return getUserProviders().parallelStream()
            .anyMatch(UserProvider::isEmailRequired);
    }
Returns whether <em>all</em> backing providers require an email address to be set on User objects. If at least
one provider does not, this method returns false.

@return true when all backing providers require an email address to be set on User objects, otherwise false.
xmppserver/src/main/java/org/jivesoftware/openfire/user/UserMultiProvider.java