An updated internet-draft is available from the IETF. This draft is a work item of the Enhancements to Internet email to support diverse service environments Working Group of the IETF.
Abstract: «The submission profile of Simple Mail Transfer Protocol (SMTP) provides a standard way for an email client to submit a complete message for delivery. This specification extends the submission profile by adding a new BURL command which can be used to fetch submission data from an Internet Message Access Protocol (IMAP) server. This permits a mail client to inject content from an IMAP server into the SMTP infrastructure without downloading it to the client and uploading it back to the server. »