This document is supposed to be documenting and explaining the formal
architecture we have, not creating new formalisms on the fly.
I thought it's supposed to be a minimal abstraction of the architecture
as it exists in common practice, not only the architecture as it's
reflected in RFCs. Some RFCs reflecting the pre-spam email world like
2821 are putting it mildly harmful in an environment with 90% of all
mail traffic considered as "unsolicited" (putting it again mildly).
Who needs a description of the old and known to be broken architecture ?