@substitution_tag.setter<EOL><INDENT>def substitution_tag(self, value):<DEDENT>
self._substitution_tag = value<EOL>
Allows you to specify a substitution tag that you can insert in the
        body of your email at a location that you desire. This tag will be
        replaced by the open tracking pixel.

        :param value: Allows you to specify a substitution tag that you can
                      insert in the body of your email at a location that you
                      desire. This tag will be replaced by the open tracking
                      pixel.

        :type value: string