I've tried to use an email action for emails with cid-embedded images and faced a problem with access to multimedia blocks.
There was issued a bug #24372 from http://forums.networkautomation.com/forum/messageview.cfm?catid=73&threadid=15237&highlight_key=y&keyword1=email
But for now at Automate Professional v. 18.104.22.168 it seems still the same problem.
Additionally, "Send Message" does not allow custom headers like
Content-Type: multipart/mixed; boundary="-------------...A128803765634794"
and how can I should send email with embedded images (without file-attachments or links to external resources, but via base64 image data)?