If we agree on a convention to compose POSTs, we can get the benefits of POE without requiring a GET first, and we can track the status of sent POSTs. We'll answer the question of "What happened to that Message-Id?" by giving it a URI.
Add an element like this somewhere, depending on the acceptance of other proposals (one example is given in PaceProtocolPaging). This Pace gives the editors carte blanche to change the field names as they see fit, so any spam about field names should be directed to them directly, rather than the atom-protocol list.
Adjust the definition of POSTing as follows:
In addition to GET, a Collection Resource also accepts POST requests. The client POSTs a representation of the desired resource to the Collection Resource. Some collections only allow members with a specific media-type and a POST MAY generate a response with a status code of 415 ("Unsupported Media Type"). In the case of a successful creation, the status code MUST be 201 ("Created").
In order to prevent duplicate POSTs, the...[more to come]