I know it a lot to ask but it would be nice to try to isolate this problem, in a reproducible manner. Try to toy around with memcached when you're about to compose a mail, etc.

We'll have to do the same thing to reproduce the issue, so a little bit of help here would be good.

I have never faced the issue directly.
The emails were forwarded to me, showing that the header had been badly initialized. One of the user who faced the problem couldn't reproduce it when I asked him to do so. But it happened to him again two days after.

Nevertheless, I'll try to catch it when occuring.

Freddy

Awaiting the opportunity to reproduce the issue, I show here an excerpt of the content of a malformed mail:

...
Received: from smtp.ensicaen.fr (smtp.ecole.ensicaen.fr [193.49.200.8])
by mailstore.ensicaen.fr (Postfix) with ESMTP id 64A95DA055
for <informatique@ecole.ensicaen.fr>; Mon, 5 Nov 2012 10:07:47 +0100 (CET)
Received: from smtp.ensicaen.fr (localhost [127.0.0.1])
by localhost (Postfix) with SMTP id F12D638E0007
for <informatique@ecole.ensicaen.fr>; Mon, 5 Nov 2012 09:58:52 +0100 (CET)
Received: from sogo.ecole.ensicaen.fr (sogo.ecole.ensicaen.fr [193.49.200.48])
by smtp.ensicaen.fr (Postfix) with ESMTPS id 2852D38E0001
for <informatique@ecole.ensicaen.fr>; Mon, 5 Nov 2012 09:58:52 +0100 (CET)
Received: from sogo by sogo.ecole.ensicaen.fr with local (Exim 4.72)
(envelope-from <nicolas.stephan@ecole.ensicaen.fr>)
id 1TVIdo-0001us-KS
for informatique@ecole.ensicaen.fr; Mon, 05 Nov 2012 10:06:44 +0100
Disposition-Notification-To: nicolas.stephan@ecole.ensicaen.fr
User-Agent: SOGoMail 2.0.2
reply-to: null@sogo.ecole.ensicaen.fr
X-Forward: 82.124.35.117
MIME-Version: 1.0
...

You wrote: "The users haven't the right to modify this field in the options." How do yo control this? Have you modified the template of the preferences module? The "reply to email" field is always editable in the official version of SOGo.

For the problematic account, does the "reply to email" field appear empty in the preferences module?

This is not account specific.
It only occures very seldom.
It can occur with every account with an empty "reply to email" field in the SOGo user settings.

In our installation approx. 10 emails per day will have that wrong "Reply-To:" out of an average of 20,000 emails send per day via SOGo.

Sorry, we could not reproduce this relyable.
But when it happens, then the string "null" is written into the emails "Reply-To:" field, which should be empty or not there at all.

Is the preference value set when you query sogo-tool?

sogo-tool user-preferences get defaults <uid> SOGoMailReplyTo

When not set, you should see :

2012-11-12 13:28:11.525 sogo-tool[14973] Value for key "SOGoMailReplyTo" not found in defaults

For the user stephan (whose part of one mail is reproduced above), the command displays:

/usr/sbin/sogo-tool user-preferences get defaults stephan SOGoMailReplyTo

Nov 12 19:50:03 sogo-tool [29443]: <0x0x2762200[SOGoCache]> Cache cleanup interval set every 300.000000 seconds
Nov 12 19:50:03 sogo-tool [29443]: <0x0x2762200[SOGoCache]> Using host(s) 'localhost' as server(s)
2012-11-12 19:50:03.522 sogo-tool[29443] Value for key "SOGoMailReplyTo" not found in defaults

Here are his preferences:

preferences = (
{
Forward = {
enabled = <I1>;
forwardAddress = (
"xxxxxxxxxxxxx@gmail.com"
);
keepCopy = <I1>;
};
SOGoContactsCategories = (
Ami,
Client,
"Coll\U00E8gue",
Concurrent,
Famille,
Fournisseur,
"Partenaire d'affaire",
Presse,
VIP
);
SOGoLanguage = French;
SOGoLoginModule = Mail;
SOGoMailComposeMessageType = html;
SOGoMailMessageCheck = manually;
SOGoMailMessageForwarding = inline;
SOGoMailShowSubscribedFoldersOnly = 0;
SOGoMailSignaturePlacement = below;
SOGoMailSortByThreads = 0;
SOGoRememberLastModule = 0;
SOGoSieveFilters = (
);
SOGoTimeFormat = "%H:%M";
SOGoTimeZone = Europe/Paris;
Vacation = {
autoReplyEmailAddresses = (
"nicolas.stephan@ecole.ensicaen.fr",
"stephan@ensicaen.fr"
);
autoReplyText = "";
daysBetweenResponse = 7;
enabled = <I0>;
endDate = <I1340748000>;
endDateEnabled = <I0>;
ignoreLists = <I1>;
};
};
},
{
Mail = {
DragHandleHorizontal = 200;
DragHandleVertical = 282;
SortingState = (
date,
0
);
};
}
);

Please try the next nightly builds. They should build this night ..

I've installed the nightly builds of the 14th of november and I'm going to log the reply-to on the mail gateway.
However, I can't redirect every user at this moment to this version since there's another bug with the enclosed files (http://www.sogo.nu/bugs/view.php?id=2096) which is too annoying.

The fix for attachments "corruption" is also included in the nightly builds. The fix is in SOPE.

Okay. The nightly build of the 14th of November is now installed and is being used by our users. Let's see.

The nightly build is up for 20 hours and there has not been any header which equals null@...
Because the bug appears so randomly, I wish other people who monitor the bug could confirm that the issue has been resolved for them too.

Reopen the ticket if the problem still occurs.

See https://github.com/inverse-inc/sogo/commit/e037ca0a4914785c4f34a50613292fa0ddc08775