[Mailman-Users] Getting duplicates when people CC list

Mark Sapiro msapiro at value.net
Mon May 1 01:42:45 CEST 2006

Tony G wrote:

>Mark Sapiro wrote:
>> Brad has already provided good information in his reply. I just want
>> to add that it looks to me like in this case, the sender's MUA is
>> actually giving the list address twice (once for To: and once for Cc:)
>> to the MTA, and the MTA is not dropping the duplicate recipient. Thus,
>> two copies of the post are actually being sent to the list.
>As I mentioned in my response to Brad, I'm not even involved in the
>discussions where I'm getting the dupes.  This would be an obvious source
>of duplication.  I'm just another quiet recipient to the list (hehe, until
>now anyway) and there's no reason for me to be explicitly identified in the
>TO or CC.

Right, but you said when you receive duplicates, the list was addressed
twice in the post, once in To: and once in Cc:. Thus, I am suggesting
that the list actually receives the post twice and sends it twice and
that's why you get two copies.

>> Do the
>> duplicates appear twice in archives and/or digests? (I think the
>> duplicate may be dropped from the archives if the message-id is the
>> same, but I'm not sure).
>No, only one copy of every post is in the archives and no one else is
>reporting dupes.

Does anyone receive digests to confirm or deny the presense of dups in
a digest. I haven't looked at the code for this right now, but as I
said, I think pipermail may drop dups from the archive, so the absence
of dups in the archive is not definitive.

There may be something here with digests too, but I don't think so.

>> Other subscribers may not see this because their incoming MTA/MUA may
>> drop duplicate message-ids.
>As with most OSS projects there is a heavy bias away from Microsoft
>software, including Outlook which I use.  Chances are slim that others in
>this OSS forum are using Outlook and thus their MUAs might be filtering
>away the problem.  So I was suspecting my MUA.  However, I do not get dupes
>when people in this mailman-users list CC the list but I do get some dupes
>from that group - obviously the same MTA/MUA tiers are involved.

The process of your not getting a dup when I address my reply to both
you and the list IS a Mailman process. You only get the direct message
from me because you have requested no dups, and Mailman sees your
address in the To: of my post so it doesn't send to you.

This is not the case on the other list where maybe the list receives
the post twice.

>This is
>why I have been suspecting something in the list software that is
>different.  Maybe there's a patch or addin that they've installed that
>corrupted this dupe-filtering code?  That's what brought me here - Until
>now I've had no idea if this was an issue specific to that group or
>something that was introduced in the v2.1.5 code that you guys would know
>or want to know about.

I don't think it's Mailman per se, but I can't be sure without knowing
what is happening. I still think it could be actually two copies of
the post reaching the list, but the fact that no one else on the list
admits to receiving dups makes this seem unlikely. I would like to
help you get to the bottom of this if I can.

I think the next thing is to collect both copies of some duplicated
posts with full headers and examine the Received: chains in each to
try to determine where the duplication is occurring. If you need help
with this, you can post headers from duplicated posts to this list or
send them to me off list, and I will try to help.

Mark Sapiro <msapiro at value.net>       The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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