def buildProtocol(self, addr):
        """
        Create an instance of a POP3 server protocol.

        @type addr: L{IAddress <twisted.internet.interfaces.IAddress>} provider
        @param addr: The address of the POP3 client.

        @rtype: L{POP3}
        @return: A POP3 protocol.
        """
        p = protocol.ServerFactory.buildProtocol(self, addr)
        p.service = self.service
        return p

        Create an instance of a POP3 server protocol.

        @type addr: L{IAddress <twisted.internet.interfaces.IAddress>} provider
        @param addr: The address of the POP3 client.

        @rtype: L{POP3}
        @return: A POP3 protocol.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/protocols.py