This plugin is available since version 4.2.0 of BwPostman. With this plugin BwPostman is able to use selected/tested content plugins of Joomla!® at the newsletter.
Because I don't know how the individual content plugins behave with BwPostman, I use whitelisting. Content plugins, which I have tested with BwPostman, are added to this list. If You use a content plugin in Your Joomla! articles, which You use in BwPostman, which are not supported by now, ask at the forum. I will see what I can do.