On Thursday, May 29, 2003 5:39 PM, Bob Wyman [SMTP:bob(_at_)wyman(_dot_)us]
wrote:
Yakov Shafronovich wrote:
According to section 4.2.2 of RFC 2821, the "550" error
code means the following:... 550 Requested action not
taken: mailbox unavailable (e.g., mailbox not found, no
access, or command rejected for policy reasons)
Ok. Perhaps it was a bit strong to say that it was a "lie."
Nonetheless, it would appear that spammer's programs are, in fact,
pretty much helpless in determing whether the "550" was issued due to a
mailbox not existing or because of "policy reasons." They are pretty
much stuck with either removing the address that failed from their
databases or providing legitimate reply-to/From addresses and trying to
deal with the C/R process. [...]
I think that there may be evidence to substantiate an argument that the SMTP
servers installed by some 'spammer' tools may actually implement a
surreptitious channel for communication of status code information, given
spammer 'adaptability' and if that is indeed the case then it is a short leap
to co-opting MS access to determine whether the response was attended by a DSN
or a C/R message. This could all be blue sky, but ...
Off-Topic: I wonder if the fact that issuing a "550" for "policy
reasons" is explicitly mentioned in RFC2821 might call into question the
validity of any patent claims that explicitly use the method defined in
the RFC... One might claim that the RFC's provision of a means to reject
for "policy reasons" did, in fact, anticipate precisely the methods
being discussed here.
precisely.
-e
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