Why do you want so much domain-specific kruft in your mail?<p>Use OmniFocus for task management, with a script or rule to move messages to Task status. Add a new iCal/vCard style micro format to specify tasks that you wish to delegate to me. No protocol needed, it is just a request after all. The protocol in delegation resides at the human layer, not the technology layer.<p>Priority etc in email makes it sound like you want to use the one piece of software to write correspondence while simultaneously managing your projects and to-do lists. Use a to-do list manager for managing tasks, use project management software for managing projects.<p>There are ways to link the lot together, but using the IMAP server as your go-to resource for everything is not the answer.<p>But I agree with you on the encryption thing.