William Herrin bill at
Sat Feb 20 04:32:10 UTC 2010

On Fri, Feb 19, 2010 at 8:35 PM, Larry Sheldon <LarrySheldon at> wrote:
> On 2/19/2010 7:20 PM, William Herrin wrote:
>> "If an SMTP server has accepted the task of relaying the mail and
>> later finds that the destination is incorrect or that the mail cannot
>> be delivered for some other reason, then it MUST construct an
>> "undeliverable mail" notification message and send it to the
>> originator of the undeliverable mail (as indicated by the
>> reverse-path)."
> Does the RFC say what to do if the reverse-path has been
> damaged and now points to somebody who had nothing
> what ever to do with the email?

Hi Larry,

Re-reading the paragraph I quoted and you repeated, I'm going to say
that the answer is "yes."

SMTP had been around for a long time when 2821 was written, as had
spam. I doubt leaving the "must" in section 3.7 was an oversight. Even
if it was, I didn't suggest rote adherence to the RFC. I said,
"reasonably compatible with RFC 2821's section 3.7." Dropping all
bounce messages on the floor -- the exact opposite of 3.7 -- is not
"reasonably compatible."

> Do your SNMP clients respond truthfully to EXPN requests?

I assume you mean "SMTP servers" here rather than "SNMP clients." 2821
rightly leaves EXPN as a "should" instead of a "must." And yes, they
respond truthfully -- with an prohibited operation error.

> I don't run any sites anymore, but when I did, unsolicited traffic
> (traffic not in response to traffic from somebody on my network) was
> blocked when detected, and remained blocked until somebody inside our
> boundary complained, and on second occurrence until my management
> directed me to remove the block.

I can't resist the set up: Maybe that's why you don't run any sites anymore.

Bill Herrin

William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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