Correct.
The file contents will pop out of whatever email plugin you’re using as a file attachment. So it will be something like.
{{["email"].["file_attachments"]}}
In that you’ll have an object that has:
file_name
file_type
file_contents
The file_contents field will have the file contents in base64 encoded bytes. That you can feed into any of the “file” plugins and save to a 3rd location that you can then reference in a message in slack.