On Mon, 4 Apr 2016, Rich Kulawiec wrote:
On Mon, Apr 04, 2016 at 05:30:13PM -0700, Andrew Daviel wrote:
I have an incident where a rejection message was forwarded to a
list, and on to other members. I don't know if that was even
mailman, but it got me thinking.
First, that's because the system which originated the rejection is broken.
On further investigation, that incident was not mailman or real mailing
list software, just a simple address expansion in sendmail to 4 people.
The sender had spoofed the sending address to the recipient, i.e. "list"
address.
All mail systems doing anti-spam/anti-virus/anti-whatever
should *always* reject (if they're going to reject) during the
SMTP conversation (a) because that's most effective and efficient
and (b) because that avoids generating a bounce message, which in
turn avoids backscatter such as you've described.
Yes; the antivirus system works like that. It was sendmail generating a
DSN back to the "sender" that caused the problem, and I think I can just
reject mail "from" that address, i.e. make it a receive-only address,
e.g. Joe and Jane both get mail to "webmaster" but reply as themselves.
Second, anything coming back should go to the Sender:, which I
believe defaults to:
LISTNAME-bounces@LISTHOST
This doesn't necessarily yield the desired outcome, e.g., it may
result in incrementing the bounce count for a subscriber when that
shouldn't really happen, but at least it avoids forwarding backscatter
to an entire mailing list.
Apologies, I confused the issue by talking about two different things,
backscatter and bounces.
My real question is, there are two types of "permanent" (500 series)
rejection - recipient problems and message problems. I want mailman to
auto-unsubscribe stale addresses after 5 (bounce_score_threshold)
bounces, but I don't want active addresses to be unsubscribed because 5
successive viruses or spams got through a relatively quiet list but were
rejected by the recipient's filters.
I wondered if that was already handled inside mailman bounce processing,
or is something that needs work.
--
Andrew Daviel, TRIUMF, Canada
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