uh, no. RFC 2822 is concerned with the user agent protocol, and it
does place a few requirements on user agents. RFC 2821 is
concerned with the mail transport protocol, so it places
requirements on MTAs.
Well, that's true, but the rest of Charles's message was exactly
right: RFC 2822 does not require (or even recommend) that user agents
unfold folded headers for any reason.
That's right, it doesn't. And that's what I meant about 2822 not being
clear (though I didn't say it that well) - it talks about how folding
affects semantics of fields, but not about whether CRLFs within folded
fields can be assumed to be significant.
But I think 2822 is *very* clear on the semantics of folding. What it
doesn't say is what (if anything) a UA should do as far as unfolding
goes for presentation to the user.
Normally we wouldn't say much about presentation anyway. What we could
say is that there is no expectation that CRLFs within header fields
are as intended by the sender.
but longstanding practice is that both UAs and MTAs can change the
folding from that supplied by the sender.
"Can change"? Of course. But that wasn't the question that was being
asked here. The question is "Should folding be changed?"
My point is that a receiving MUA should not assume that any CRLFs
present in a header field were intended to be there by the sender.
Therefore there is no obligation to preserve those CRLFs in presentation,
and MUAs are free to re-fold fields for the purpose of presentation
as they deem appropriate.
Keith