Given the primary protocol goal of avoiding server-side message parsing, I believe the best solution is to require the source of the message to provide an envelope recipient. This would cause restrictions on delivery (must use BikINI to deliver messages, or a special delivery agent, or a client which can provide recipient information), but would also allow a simplicity of implementation which is seductive.

The MTA should know the envelope recipient at that time. If a client is placing the message (for example, one just sent or being sent via "SEND"), then the client knows the envelope recipient from the clients perspective.

While the fix to both this and the envelope sender is not ideal, it will be sufficient until I get/am given a better idea. - dave

Issue done.