'Validate the address for which the message is destined.
@type user: L{User}
@param user: The address to validate.
@rtype: no-argument callable
@return: A C{Deferred} which becomes, or a callable which
takes no arguments and returns an object implementing C{IMessage}.
This will be called and the returned object used to deliver the
message when it arrives.
@raise SMTPBadRcpt: Raised if messages to the address are
not to be accepted.'

def validateTo(self, user):

    if (self.delivery is not None):
        return self.delivery.validateTo(user)
    raise SMTPBadRcpt(user)
