Yes. Relays MUST simply relay messages. Only when a message
has reached an MTA under the *direct control of the recipient*
can other actions be taken. Is everybody happy with that
phrase before I start sprinkling it throughout the draft? :)
I don't mind the phrase, but you need to define it somewhere. For
instance, does "direct control of the recipient" allow an ISP to
make assertions on behalf of its customers? Does it allow a
business's SMTP server to make assertions on behalf of its
employees?
Oof. No way am I going to try and define that concept. :)
How about a reference to section 7.7 of 2821, "Scope of
Operation of SMTP Servers"? That seems to cover this
situation pretty carefully and I can quote the whole
section (it only has 2 paragraphs).
I guess I think it is a stretch to say that a site-wide policy of
filtering some messages based on sender-selected labels is an
"operational or technical reason". Yes, there are unfortunately
cases when sites have legitimate reasons for refusing, or even
discarding, mail that meets certain criteria - but I seriously
doubt that sender-selected labels are useful criteria for choosing
to employ such drastic measures. And while I do recognize that
some sites have valid reasons for setting policies on behalf of
all of their users, I don't want this document to encourage ISPs
to do this.
But to me, "direct control of the recipient" means that the
recipient (NOT the site) chooses the criteria by which messages
are rejected.
I don't think the 2nd paragraph of section 7.7 is apropos here,
or at least, it's talking about something different then what I
thought we were talking about.
I don't think this is quite there yet, but here's a stab at text:
- Intermediaries that aren't acting on behalf of either the sender or
recipient SHOULD NOT filter based on SOLICIT= or Solicitation: or on
Received: fields
- A per-server policy SHOULD NOT be specified unless it is reliably
known that the policy is appropriate for all users of that SMTP server,
including users whose mail is locally delivered and users whose incoming
mail is routed through the local server for delivery on other servers.
- A per-recipient policy SHOULD be under direct control of the
recipient, meaning that the recipient has consented to the policy
and has the ability to change or remove the policy.
It is recognized that there may be valid operational reasons for
refusing mail based on its content. As a general rule that any server
MAY refuse to accept mail for any reason if there is a technical or
operational requirement to do so (such as resource exhaustion or hostile
attack) [ref 7.7 of rfc 2821]. However, the SMTP extension described
in this document is not intended as a general-purpose mechanism for
ameliorating operational difficulties and such mechanisms are outside
the scope of this document.