Various forms of machine-readable message have been realized on top of the versatile email standards. Some examples are:
- Abuse Reporting Format (ARF) (RFC 6650)
- Calendaring invites (“iMIP”; RFC 2447)
- Indicating Summary Reaction to a Message (RFC 9078)
- Message Delivery Notifications (MDNs; RFC 8098)
- Military Message Handling System (MMHS) Header Fields (RFC 6477)
- One-click unsubscribe from email lists (RFC 8058)
RFC-based structured email workflows can considerably extend the usefulness of email technology. Elaborate specification is particularly useful in highly interactive processes, such as meeting organization, which may involve various different software systems or parties.
RFC-based specification is time-consuming and rather slow, as is its adoption by vendors. Due to RFCs evolving mostly independently of each other, vendor implementations might be inconsistent and inefficient.