TYPO3 Core

According to the documentation (https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/ApiOverview/Mail/Index.html#how-to-add-inline-media) it is possible to add an image inline via attachment. But this is only possible in PHP if writing an own extension. If using an existing extension or system mails it is not possible to include an image that way. It would be great to do that in typoscript or AdditionalConfiguration.php.