Great Circle Associates List-Managers
(July 1998)

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Subject: Listserv's violation of RFC821
From: Norbert Bollow <nb @ thinkcoach . com>
Date: Fri, 31 Jul 1998 19:28:36 +0200
To: list-managers @ GreatCircle . COM, Eric Thomas <ERIC @ VM . SE . LSOFT . COM>
In-reply-to: <> (
Prefer-language: de, en, fr

Ronald F. Guilmette <> wrote:

> Speaking of ``probes'', I have just been dealing with a problem on my end
> that is rather annoying [..]
> The problem is that 9apparently) Listserv cane be told (by the list owner)
> to perform some sort of a ``probe'' on a given address which may be bad,
> and it will then go and try to do that.
> Now get this... if the probe FAILS... which is to say if the address is
> in fact bad... then it appears that Listserv then tries to send a ``probe
> No, I'm not making this up.
> That doesn't bother me so much as the WAY in which these idiotic ``probe
> failed'' messages are sent... They appear to be sent with a null/empty
> envelope return address, thus making them (in some ways related to spam
> filtering) indistinguishable from ordinary Mailer-Daemon bounces for mail
> which was sent *from* my system to someplace else.

Eric Thomas <ERIC@VM.SE.LSOFT.COM> (the author of Listserv) replied:

> it  should be fairly obvious why you want to send  a "probe failed"
> message with MAIL FROM:<>, in fact it  borders on self-evidence. I'm
> sure someone else on this list will post an  explanation if you
> really can't figure it out on your own after making a *genuine*
> attempt (hint: what is the typical criterion for auto-delete on a
> typical LISTSERV list?) 

Although I definately do not agree with this practice, it is indeed
obvious why Eric Thomas wants to send his "probe failed" messages with
MAIL FROM:<> - it is because otherwise it's extremely likely that the
"probe failed" message will bounce, and the list-owner doesn't want to
be bothered by the bounce of the "probe failed" message.

Sending a "probe failed" message in the first place is not 'idiotic'
light it might appear at first glace - in fact some kind of "probe
failed" message is a necessecity in any system which does automatic
bounce processing. The reason is that there are broken gateways and
misconfigured MTAs which send a "delivery failed" bounce even if the
message was in fact delivered to the recipient. In this kind of 
situation the "probe failed" message is important since it gives a clue
to the subscriber about what is going on.

However I agree with Ron that

a) Sending the "probe failed" message immediately after the probe has
   failed is not a terribly good idea; it is advisable to delay it a
   couple of hours or a day.

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

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.

Eric also wrote:

> It seems that my signoff request needs to be approved by the list
> owner (?), but consider me gone.

I am surprised to see you leave the list-managers list in reaction
to Ron's criticism. Nobody asks you to waste your time on a flame
war, but when your software creates problems for others, and these
problems can be solved by making your software conform to well-
established internet standards, then it is your responsibility as a
net citizen to fix the software, and _not_ run away from the mailing
list where the issue is discussed.

-- NB.

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