[Mailman-Users] Random duplicate message to subscribers

bjames at cisco.com bjames at cisco.com
Tue May 8 00:16:12 CEST 2007

--> Jason LaMar wrote:
--> >We have a fairly large list (more than 26,000 subscribers), and recently it
--> >appears a very small fraction of the subscribers have started receiving
--> >duplicate messages -- sometimes as many as a dozen or more. This behavior
--> >just started happening within the last couple of weeks, and it seems to only
--> >impact a minute and random subset of the subscribers. Anyone seen similar
--> >behavior or have suggestions on the most effective way to troubleshoot this?
--> There have been a number of discussions regarding similar things in 
--> the last few months. IIRC almost all of them were due to filter rules 
--> on the receiver end.
--> A search of the list archives for "duplicate posts" or something 
--> similar ought to turn up the discussions. I don't know if anything 
--> exists in the FAQ regarding this. However, it is highly unlikely that 
--> Mailman is the culprit here. A check of the Mailman SMTP log and MTA 
--> logs should be able to determine if multiple copies are being sent.
--> Far more likely is that the subscribers are getting multiple copies 
--> of replies to their posts or they have filter rules that are copying 
--> the posts instead of moving them.

I also suggest checking whether the subscribers receiving multiple
copies use the same ISP (or the same small set of ISPs).  I have seen
several ISPs who install "upgrades" to their MTAs and cause this symptom.
One of the root causes has been receiving MTAs that terminate the
MTA-to-MTA TCP connection before the SMTP final acknowledgement has
been processed; this causes a properly behaving sending MTA to believe
that the message handoff was not* successful, and retransmit.

If you can get the users to forward you the duplicate messages, with
complete mail headers, you can sometimes spot this behavior in the
"Received:" fields.  For example, if the ISP has multiple mail
exchangers ("nslookup -query=mx userisp.domain"), the duplicate
copies may come through different mail exchangers in close time
sequence, as the sending MTA tries one mail exchanger after the


--> >We're running version 2.1.5 on Red Hat Linux ES, and we've also had a few
--> >runaway Python processes in the last couple of months that forced us to
--> >restart the server. Perhaps this is all related and we just need to upgrade
--> >to 2.1.9. Anybody happen to have a pre-built RPM for RHEL 4 with the latest
--> >release?
--> Are you committed to Red Hat's way of doing things? If you don't 
--> really care about their file hierarchy system, I would suggest 
--> dumping the RPM and compiling from source yourself. I've done a 
--> source install of various versions of Mailman on both an RHEL 4 and 
--> an RHEL 6 system and never had a problem with doing so.
--> Otherwise, you are pretty much doomed to being behind a bit on 
--> releases if you rely on a package distribution of Mailman.
--> Dragon
--> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-->   Venimus, Saltavimus, Bibimus (et naribus canium capti sumus)
--> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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