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Re: DSN requests via headers?

2000-12-18 14:21:40
Normal people measure the reliability of a return-receipt system as the
chance of finding out whether the message was successfully delivered.

An end-to-end design is much better for this than a link-level design:
it's much easier to implement, and it doesn't need support from relays.

DSN proponents have a different notion of reliability. They think
they've done their job if the user receives a bounce saying ``This
message was relayed to a system that won't tell you what happens.''

In theory, a link-level system can guarantee that the user will always
receive some sort of bounce, while an end-to-end system can't. So DSN
proponents say that link-level systems are ``reliable'' and end-to-end
systems are ``inherently unreliable,'' even though users actually find
end-to-end systems more reliable.

(In fact, DSN proponents are not telling the truth when they make this
guarantee. Sendmail 8.6.10 through 8.9.3 with the popular noreceipts
option will accept DSN requests and then throw them away.)

This has nothing to do with Alvestrand's screwed-up layering concepts,
or with minor syntax details of where link-level envelope information
appears in an SMTP conversation.

---Dan

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