This documentation is not using the current rendering mechanism and will be deleted by December 31st, 2020. The extension maintainer should switch to the new system. Details on how to use the rendering mechanism can be found here.
Please see/report problems in the direct_mail project page on TYPO3 Forge
You may get support in the use of this extension by subscribing to news://news.netfielders.de/typo3.projects.direct-mail .