Re: confirmation

[Randall Gellens]

At 11:29 AM +0100 2/9/03, Cliff Sarginson wrote:

  > DSNs are requested at the SMTP (transport) level, and can result in

 positive acknowledgment of a message's arrival at the last server
 (the user's spool).  It must be supported by the originating
 submission program, and all servers in between.  It does not indicate
 if the message was ever downloaded by the user, but it can give a
 reasonable indication that the message wasn't lost en route.

 Mmm. As you are implying this does expect co-operation all the way down
 the line, plus the co-operation of the end-receiver.

DSNs rely on cooperation from every server en route, including the final one. To be more accurate, requesting non-default DSN behavior requires this. By default, most servers generate failure DSNs which include the full original message. The DSN extension mechanisms allows the originator to request various non-default behavior, such as success, relay, or delay DSNs, and can request that only the headers of the original message be included. In addition, the extension mechanism allows the originator to supply a unique identifier which will be included in the DSN. These mechanisms are great for mailing lists, for example, but could also be handy for user agents to, for example, indicate to the author the current known status of the delivery of a message to each recipient (success, failure, delay, relay). Relay status indicates that the message was passed to a server which does not support the DSN extensions.

  I personally never
 allow DSN messages .. since I politically disapprove of them (but that
 is another story :) ..

What about them do you disapprove of?

 They can generate a fair amount of more or less
 white-noise email,

have you seen this?

  and are unreliable at best. I don't think they can be
 relied upon as proof of anything very much anyway.

I'm not sure DSNs are ever appropriate as "proof" of anything. Their reliability is directly related to the proportion of servers that support them. They can be useful. Certainly a failure DSN is very useful. A success DSN at least tells you the message made it that far. A relay DSN doesn't tell you much. No DSN tells you anything about the disposition of the message, by design.

--
Randall Gellens
Opinions are personal; facts are suspect; I speak for myself only
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