I am trying to send Confidential emails via gmail, although I am not sure it is supported. Via the gmail API, the User.messages fields do not seem to indicate whether an email is confidential or not. I retrieved a confidential and regular email via the v1 gmail api get method and the messages are identical. Is there a way send a confidential gmail email, either with the official api or other service?
To my knowlage you can't send messages with "Confidential mode" through the Gmail API.   This is not currently supported.
Send Confidential email through gmail api