Reference to an attachment prepared with the large-attachment upload API.
https://developer.nylas.com/docs/v3/email/send-large-attachments/
Optional
Content ID to reference from the message body when displaying the file inline.
The attachment ID returned by a completed upload session.
Reference to an attachment prepared with the large-attachment upload API.
See
https://developer.nylas.com/docs/v3/email/send-large-attachments/