The mailing list for listmasters using Sympa

["Ward, Michael" <address@concealed>]

Hi,

Thanks for the responses. After the first comment, I did a bit more log 
trawling to find out what really going on. I verified what Adam said is 
correct, Sympa did indeed send me multiple emails.

Looks like Exchange (and obviously other mail systems) is detecting the 
duplicate messages and only delivering one of them. More details on how it's 
doing this here: http://msexchangeteam.com/archive/2004/07/14/183132.aspx

So according to the details there, if one of the lists were moderated, the 
user will only receive one message - as long as the moderated message is 
released within one hour of the other message.

Good to understand how this works now - I can now tell my users why they're 
only receiving one email when they're expecting multiples with some 
confidence!

Thanks for the help,
Michael Ward


-----Original Message-----
From: Cefiar [mailto:address@concealed]
Sent: Thursday, 8 May 2008 1:25 p.m.
To: address@concealed
Subject: Re: [sympa-users] Recipients that are members of multiple Sympa lists

On Thursday 08 May 2008 11:02:04 Adam Bernstein wrote:
> >  From my testing, I can see that if a message is sent to multiple Sympa
> > lists and a recipient is a member of more than one of these lists, only
> > one copy of the message is received.
>
> Nope, it doesn't have any way to de-duplicate deliveries like that.
> Subscriber to multiple lists receives a copy from each one.  Must be
> something else going on in your testing.

FWIW: Some mail storage systems do this deduplication automatically. One of
the many ways to identify a duplicate is using the Message-ID: header.

If the list emails all go out with the same Message-ID header (which, given
they're the same originating email, and the Message-ID header is preserved,
should always be the case), then it's quite possible that this can happen.
Same thing happens if your MTA decides to deliver to multiple "local"
addresses (local to the mail storage system) at the same time.

I tripped over this issue with Cyrus, which does this by default (and caused a
fair bit of CC'd mail to vanish inconsistently). At least in the case of
Cyrus, this behaviour can be changed. If the system has some other type of
storage engine (eg: a built in proprietary one), then you should check if
there is an option somewhere for it. Hopefully you won't be out of luck.

PS: Another (slim) possibility is that each message got delivered separately,
and that one has hit a slow MX somewhere along the line. I've had this with a
number of ISP email accounts, where one of the MX's for their domain seems to
hold on to mail for 12-24 hours for absolutely no conceivable reason before
forwarding it on to another MX or to their storage back-end.

--
 Stuart Young - aka Cefiar - address@concealed