@Override
    public boolean isMultipleSubscriptionsEnabled() {
        return false;
    }
Returns true if the prober is allowed to see the presence of the probee.

@param prober the user that is trying to probe the presence of another user.
@param probee the username of the uset that is being probed.
@return true if the prober is allowed to see the presence of the probee.
@throws UserNotFoundException If the probee does not exist in the local server or the prober
        is not present in the roster of the probee.
xmppserver/src/main/java/org/jivesoftware/openfire/pep/PEPService.java