John Levine wrote
Again, I don't see how that contstrains the address beyond
requiring that it accept bounces.
Standard quote: "the originator as indicated in the reverse
path". It *identifies* the originator, it's not designed to
be something like a Message-ID.
As Ned said, this is a major deviation from what an envelope
sender address used to be for some decades, and it's IMO not
*obvious* how it works in conjunction with RFC 3834 + SIEVE.
Likely it does, otherwise you'd know these problems already,
but you could have missed obscure issues with the completely