[Mailman-Users] Getting duplicates when people CC list

[Tony G]

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.

> 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.
 
> 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.  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.

Thanks again.