Upload data to mailbox
Write backend code to create a temporary file, write a simplex stream to the file, and upload the file to the user's own mailbox or a contact's mailbox.
Depends on #1804 (closed).
Write backend code to create a temporary file, write a simplex stream to the file, and upload the file to the user's own mailbox or a contact's mailbox.
Depends on #1804 (closed).