Get a MIME Message

This method is used to retrieve a DataMotion message in standard MIME format.
Senders and recipients are the only users that have access to the message and will be permitted to retrieve basic DataMotion header information and the Security Envelope.
The message sender is the only user that will be permitted to retrieve detailed tracking information.
When a message is retrieved using this function, tracking information will automatically be written indicating the message was read by the recipient.
A session key must be submitted via the X-Session-Key header.
The request body should be left empty.
The message ID of the message you'd like to get the MIME format of must be passed in the URL of this method.
A successful transaction will receive a 200 status code.