> b) Such a "probe failed" message MUST NOT be sent with MAIL FROM:<>
> In fact, RFC821 is very clear that e-mail messages are supposed to
> have a good reverse-path
>
> : The argument to the MAIL command is a reverse-path, which specifies
> : who the mail is from.
>
> and later the exception of bounces is introduced with the words
>
> : prevent loops in error reporting is to specify a null reverse-path
> : in the MAIL command of a notification message. When such a
> : message is relayed it is permissible to leave the reverse-path
> : null.
>
> (Note: By section 5.3.3 of RFC1123 in this case the reverse path MUST
> be null).
>
> Note that Listserv's behavious cannot be defended by classifying the
> "probe failed" message as a bounce, because then it'd be a bounce of
> the bounce of the probe, and hence be illegal by section 5.3.3 of
> RFC1123.
>
> Conclusion: Since Listserv violates RFC821 which is a generally
> accepted standard and this violation makes life unneccessarily hard
> for those who develop anti-spam software, Listserv should be fixed.
RFC 821 isn't the whole story on this issue. Other RFCs have introduced
the principle that some messages may be sent with a null MAIL FROM.
RFC 1894 states that Delivery Status Notifications (DSNs) are to be sent
with a null MAIL FROM address. While a DSN may be a bounce message, it
may also be a report of successful delivery. RFC 2298 states that
Message Disposition Notifications (MDNs) are also to be sent with a
null MAIL FROM address. In no case is an MDN a bounce message. So the
principle that status reports can be sent with a null MAIL FROM address
is well established. Both RFCs 1894 and 2298 are standards-track
documents.
Also note the following text in RFC 821:
MAIL (MAIL)
... In some types of error
reporting messages (for example, undeliverable mail
notifications) the reverse-path may be null (see Example 7).
This suggests that there could be messages other than bounces that
have a null MAIL FROM.
LISTSERV's "probe failed" message sounds to me like an "error
reporting message".
