def cap_EXPIRE():
        """
        Return the minimum number of days messages are retained.

        @rtype: L{int} or L{None}
        @return: The minimum number of days messages are retained or none, if
            the server never deletes messages.
        """

        Return the minimum number of days messages are retained.

        @rtype: L{int} or L{None}
        @return: The minimum number of days messages are retained or none, if
            the server never deletes messages.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/interfaces.py