OPES/SMTP Bypassing and Tracing

Hi,

when reviewing draft-ietf-opes-smtp-00 please focus on section 4
"Tracing" and section 5 "Bypassing" - there are some notes "to discuss
on mailing list".

In former drafts we concentrated on classic
client-sends-request-to-server-which-replies-with-a-response
environments.
Here and there, we have indications that other application protocols
exist, for example:
   RFC3914: "Moreover, some application protocols may not have explicit
responses..."

In SMTP tracing information for the email recipient is trivial. But
reliable notifications for the email sender are a problem (a general
problem with SMTP not only for OPES).
How does that correspond to the IAB considerations?
What do you think about DSN (RFC1891) and Message Tracking (RFC3885) to
build on for OPES/SMTP?

Bypass is the other way arround.
OPES bypass is usually client controlled. Does that mean email recipient
controlled?
It is hard to check the client's bypass requests in a sender centric
OPES system.
What do you think about the bypass section in draft-ietf-opes-smtp-00?
Does that work or do we need an out-of-band solution?

Regards
Martin