You are in right path in creating a message in specified folder in outlook. when you create a message, by default it will be drafted in Drafts folder. You can move the message to specified folder using /messages/message-Id/move endpoint. However, isDraft value will be in true state until you send the message using /messages/message-Id/send and this is expected.

In my case, I used sample python code to convert MIME message to Base64-Encoded MIME String.

import  base64
from  email.message  import  EmailMessage

msg  =  EmailMessage()
msg['From'] =  '[email protected]'
msg['To'] =  '[email protected]'
msg['Subject'] =  'Test Email via Microsoft Graph API'
msg.set_content('Hi...This is the body of the email in MIME format. \n  \n Thanks')

raw_bytes  =  msg.as_bytes()
base64_encoded  =  base64.b64encode(raw_bytes).decode('utf-8')
print("Base64-Encoded MIME String:\n")
print(base64_encoded)

• I called https://graph.microsoft.com/v1.0/users/[email protected]/messages endpoint to create a message using base64 encoded MIME string from previous step. Request Body: base64 encode string Request Header: Content type = text/plain

• Now I called https://graph.microsoft.com/v1.0/users/[email protected]/messages/{message-id}/move to move to specified folder. Request Body: { "destinationId": "< Destination folder Id>"} Request Header: Content type = application/json

• Next I called sent endpoint to send the message and read the email content using https://graph.microsoft.com/v1.0/me/messages?$search="<Subject mail>"

Successfully created message and sent