Totally naive questions: Could we come up with a new protocol (possibly based on SMTP/IMAP/whatever), that would only guarantee to get your email to its recipi

Totally naive questions: Could we come up with a new protocol (possibly based on SMTP/IMAP/whatever), that would only guarantee to get your email to its recipient if you included some sort of token generated by the recipient and given to you? Something where you could text/message/whatever a unique token to a friend/business/etc. and then they can send you email? And if you email someone, your outgoing email includes the token necessary for them to reply? The contents (including who it’s being sent to) would be encrypted by default rather than being plain text that anyone in between sender and recipient (or at least sender and recipient servers) could read. Is something like that possible? Obviously at first nobody would have it implemented, so you’d have to get developers interested in writing server and client software, and convince people and companies to use it instead of or in addition to regular email. But I wonder how many people would be interested in such a system and whether it would be workable?