Confirmed.
This happens because BB Mail Client updates the Sent folder via AS just after the mail sending, and get this sent email in text mode without headers(Bugs: 3143,3146,3149). Such as In-Reply-To.

I've provided temp. workaround in 3146

https://github.com/inverse-inc/sogo/commit/f5607b3e857270f2efdf7c28a629d93b54029d86

An additional fix was pushed:

https://github.com/inverse-inc/sogo/commit/e71a1c9974cc6f0177b50065a173aa37963cc159

Mail thread still broken. Not sure it's a BlackBerry 10 issue or a SOGo issue, hope SOGo developers can help figure it out. Once we confirm it's a BlackBerry issue, i will try to report this in BlackBerry forum.

Steps to reproduce this issue:

1: Send an email with BlackBerry 10 (device: Passport, OS: 10.3.2.2204) to myself. I received this email in seconds, with mail header:

Message-ID: <1st@[my_domain]>

2: Reply to this first received email, received in seconds with below mail headers:

Message-ID: <2nd@[my_domain]>
In-Reply-To: <1st@[my_domain]>

So far so good, emails are grouped in ONE thread.

3: Reply to the latest reply, received in seconds with below mail headers:

Message-ID: <3rd@[my_domain]>
In-Reply-To: <2nd@[my_domain]>

This reply is grouped in a new thread.

The working solution is:

*) New reply email should write ALL message-id exist in head 'Message-ID' and 'In-Reply-To' of original mail to 'In-Reply-To' in new email.

*) New reply email should write ALL message-id exist in head 'Message-ID' and 'References' of original mail to 'References' in new email.

For example:

In-Reply-To: <1st@[my_domain]> <2nd@[my_domain]> <3rd@[my_domain]>
References: <1st@[my_domain]> <2nd@[my_domain]> <3rd@[my_domain]>

This way, all MUAs should correctly detect the thread.

I searched SOGo github repo, i guess we can improve it in file ActiveSync/SOGoActiveSyncDispatcher.m, line 2606:
https://github.com/inverse-inc/sogo/blob/5ad36626406e55e82867351c9775a357748e2b28/ActiveSync/SOGoActiveSyncDispatcher.m#L2606

Write Message-ID and In-Reply-To of old emails to In-Reply-To in new email.
Write Message-ID and References of old emails to References in new email.

Reference: http://cr.yp.to/immhf/thread.html

Update: In-Reply-To should contain only the last message id, but References should contains all.

https://github.com/inverse-inc/sogo/commit/4e7a3ce5fac99efd712168986016295e8e47629a

If no References: header, SOGo should create it and append value of In-Reply-To: and Message-ID: in References.

This issue is still reproducible in SoGo 2.3.1.

Additional fix pushed: https://github.com/inverse-inc/sogo/commit/2bccfcb725e9269e01df11ef3b2c03eba675fc4c

Please try the upcoming nightly builds, available in about 12 hours from now.

Still not solved with the latest nightly build. I'm now confused which one causes this issue, SOGo, BlackBerry 10, or MUA ... Will try to figure it out.

Any updates on this?

Still not solved with the latest sogo-2.3.5.

I've an update on the issue.
It seems like latest SoGo (>2.3) almost fixed the issue.
Only third outgoing email in the thread have no earlier Message IDs, so the thread breaks.
Just like SoGo removes them for some reason.

Dear support,

Any update on this issue? Current status is just like @st41ker said: "Only third outgoing email in the thread have no earlier Message IDs, so the thread breaks."

Can you please reproduce the problem with SOGoEASDebugEnabled = YES and upload the sogo.log. I'm not able to reproduce the problem and what to see the difference compared to my env. The log with the cmd=sendmail requests would help to understand the problem.

Here's the log of 'Cmd=SendMail' request, let me know if it's not enough:

###############
Mar 10 08:43:19 sogod [1356]: mail.mydomain.com "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=Sync&DeviceType=BlackBerry&User=z
hb%40mydomain.com&DeviceId=BB2AAB1F7E HTTP/1.0" 200 0/77 0.509 - - 0
Mar 10 08:43:20 sogod [1356]: <0x0x556c3f18d458[SOGoActiveSyncDispatcher]> EAS - request for device BB2AAB1F7E: <?xml version
="1.0"?>
<!DOCTYPE ActiveSync PUBLIC "-//MICROSOFT//DTD ActiveSync//EN" "http://www.microsoft.com/&quot;>
<SendMail xmlns="ComposeMail:">
<ClientId>1456153614-1278</ClientId>
<SaveInSentItems/>
<MIME>Q29udGVudC1UeXBlOiB0ZXh0L2h0bWw7IGNoYXJzZXQ9InV0Zi04Ig0KTUlNRS1WZXJzaW9uOiAxLjANCkNvbnRlbnQtVHJhbnNmZXItRW5jb2Rpbmc6IH
F1b3RlZC1wcmludGFibGUNClgtQ2xpZW50LUlEOiAxMjc4DQpYLU1haWxlcjogQmxhY2tCZXJyeSBFbWFpbCAoMTAuMy4yLjI4NzYpDQpNZXNzYWdlLUlEOiA8MjA
xNjAzMTAwMDQzMTkuNTM5MDQyMS43MDU1Ny4xMjc4QGlyZWRtYWlsLm9yZz4NCkRhdGU6IFRodSwgMTAgTWFyIDIwMTYgMDg6NDM6MTkgKzA4MDANClN1YmplY3Q6
IFRlc3QgZnJvbSBiYjEwDQpGcm9tOiB6aGJAaXJlZG1haWwub3JnDQpUbzogWmhhbmcgSHVhbmdiaW4gPHpoYkBpcmVkbWFpbC5vcmc+DQoNCjxodG1sPjxoZWFkP
jxtZXRhIGh0dHAtZXF1aXY9M0QiQ29udGVudC1UeXBlIiBjb250ZW50PTNEInRleHQvaHRtbDsgY2hhcnNldD0NCj0zRHV0Zi04Ij48c3R5bGU+IGJvZHkgeyAgZm
9udC1mYW1pbHk6ICJDYWxpYnJpIiwiU2xhdGUgUHJvIixzYW5zLXNlcmlmLCJzYT0NCm5zLXNlcmlmIjsgY29sb3I6IzI2MjYyNiB9PC9zdHlsZT4gPC9oZWFkPiA
8Ym9keSBsYW5nPTNEInpoLUNOIiBzdHlsZT0zRCIiPj0NCjxkaXY+U2VudCBmcm9tIG1vYmlsZTwvZGl2PjxkaXY+PGJyPjwvZGl2PjxkaXY+LS0tLTxicj5aaGFu
ZyZuYnNwO0h1YW5nYmluLD0NCiZuYnNwO2ZvdW5kZXImbmJzcDtvZiZuYnNwO2lSZWRNYWlsJm5ic3A7cHJvamVjdDombmJzcDtodHRwOi8vd3d3LmlyZWRtYWlsL
j0NCm9yZy88YnI+VGltZSZuYnNwO3pvbmU6Jm5ic3A7R01UKzgmbmJzcDsoQ2hpbmEvQmVpamluZykuPGJyPkxvb2tpbmcmbmJzcDtmbz0NCnImbmJzcDthbiZuYnNwO29wcG9ydHVuaXR5Jm5ic3A7dG8mbmJzcDttb3ZlJm5ic3A7dG8mbmJzcDthbm90aGVyJm5ic3A7Y291bj0NCnRyeS48L2Rpdj48L2JvZHk+PC9odG1sPg==</MIME>
</SendMail>

Mar 10 08:43:20 sogod [1356]: mail.mydomain.com "POST /SOGo/Microsoft-Server-ActiveSync?Cmd=SendMail&DeviceType=BlackBerry&User=zhb%40mydomain.com&DeviceId=BB2AAB1F7E HTTP/1.0" 200 0/961 0.480 - - 64K
Mar 10 08:43:22 sogod [1356]: <0x0x556c3f12c488[SOGoActiveSyncDispatcher]> EAS - request for device BB2AAB1F7E: <?xml version="1.0"?>
<!DOCTYPE ActiveSync PUBLIC "-//MICROSOFT//DTD ActiveSync//EN" "http://www.microsoft.com/&quot;>
<Sync xmlns="AirSync:">
<Collections>
<Collection>
<SyncKey>1457477752</SyncKey>
<CollectionId>vevent%2FB87704E5-3FA2-4644-A386-1358E45F39DA</CollectionId>
<GetChanges/>
<WindowSize>25</WindowSize>
<Options>
<Class>Calendar</Class>
<FilterType>6</FilterType>
<BodyPreference xmlns="AirSyncBase:">
<Type>1</Type>
<TruncationSize>1048576</TruncationSize>
</BodyPreference>
</Options>
</Collection>
</Collections>
</Sync>
###################

I docoded the content inside <MIME></MIME> block, here's the mail header part:

###################
Content-Type: text/html; charset="utf-8"
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
X-Client-ID: 1278
X-Mailer: BlackBerry Email (10.3.2.2876)
Message-ID: <20160310004319.5390421.70557.1278@mydomain.com>
Date: Thu, 10 Mar 2016 08:43:19 +0800
Subject: Test from bb10
From: zhb@mydomain.com
To: Zhang Huangbin <zhb@mydomain.com>

###################

Did some more testing with a Gmail account, i think the problem is email sent with mobile device + SOGo doesn't have 'References:' header. Below are headers of sent and received emails in order:

1: Gmail -> Me
2: BB10 -> Gmail (WARNING: No 'In-Reply-To:' and 'References:')
3: Gmail -> Me (Note: this is 3rd email in the mail conversation, and thread broke on BB10 with this email. Also, email sent by Gmail contains 'In-Reply-To:' and 'References:')
4: Me (Mac OS X, Mail.app) -> Gmail (Note: mail composed by Mail.app also contains 'In-Reply-To:' and 'References:')
5: Gmail -> Me (has 'In-Reply-To:' and 'References:')

MIME-Version: 1.0
Received: by 10.107.157.68 with HTTP; Wed, 9 Mar 2016 17:21:18 -0800 (PST)
Date: Thu, 10 Mar 2016 09:21:18 +0800
Delivered-To: user@gmail.com
Message-ID: <CAJzwPOOf=tbQyBtYuy8MQtgeAmxBZF8Lx4+6Q_D9huQQ31gPGg@mail.gmail.com>
Subject: test
From: Zhang Huangbin <user@gmail.com>
To: Zhang Huangbin <zhb@mydomain.com>
Content-Type: text/plain; charset=UTF-8

Content-Type: text/plain; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
X-Client-ID: 1304
X-Mailer: BlackBerry Email (10.3.2.2876)
Message-ID: <20160310012216.5374035.64004.1304@mydomain.com>
Date: Thu, 10 Mar 2016 09:22:16 +0800
Subject: Re: test
From: zhb@mydomain.com
To: Zhang Huangbin <user@gmail.com>

MIME-Version: 1.0
Received: by 10.107.157.68 with HTTP; Wed, 9 Mar 2016 17:22:41 -0800 (PST)
In-Reply-To: <20160310012216.5374035.64004.1304@mydomain.com>
References: <20160310012216.5374035.64004.1304@mydomain.com>
Date: Thu, 10 Mar 2016 09:22:41 +0800
Delivered-To: user@gmail.com
Message-ID: <CAJzwPONLqCNx32fs3_eDwBjqtk0mePa-cxvXzeQ2=-ATczkPKg@mail.gmail.com>
Subject: Re: test
From: Zhang Huangbin <user@gmail.com>
To: Zhang Huangbin <zhb@mydomain.com>
Content-Type: text/plain; charset=UTF-8

Delivered-To: user@gmail.com
Received: by 10.107.29.207 with SMTP id d198csp183748iod;
Wed, 9 Mar 2016 17:26:21 -0800 (PST)
X-Received: by 10.182.33.166 with SMTP id s6mr469730obi.30.1457573181534;
Wed, 09 Mar 2016 17:26:21 -0800 (PST)
Return-Path: <zhb@mydomain.com>
Received: from mail.mydomain.com (mail.mydomain.com. [45.56.127.226])
by mx.google.com with ESMTPS id oi2si718451obc.104.2016.03.09.17.26.21
for <user@gmail.com>
(version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
Wed, 09 Mar 2016 17:26:21 -0800 (PST)
Received-SPF: pass (google.com: domain of zhb@mydomain.com designates 45.56.127.226 as permitted sender) client-ip=45.56.127.226;
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of zhb@mydomain.com designates 45.56.127.226 as permitted sender) smtp.mailfrom=zhb@mydomain.com;
dkim=pass header.i=@mydomain.com
Received: from mail.mydomain.com (mail.mydomain.com [127.0.0.1])
by mail.mydomain.com (Postfix) with ESMTP id 377F34212
for <user@gmail.com>; Thu, 10 Mar 2016 01:26:21 +0000 (UTC)
Authentication-Results: mail.mydomain.com (amavisd-new);
dkim=pass (1024-bit key) reason="pass (just generated, assumed good)"
header.d=mydomain.com
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mydomain.com; h=
x-mailer:to:references:message-id:content-transfer-encoding:date
:date:in-reply-to:from:from:subject:subject:mime-version
:content-type:content-type; s=dkim; t=1457573180; x=1458437181;
bh=frcCV1k9oG9oKj3dpUqdJg1PxRT2RSN/XKdLCPjaYaY=; b=rkk2BDBdMNFd
btGVpajZcnYpXSBZCshNfWa7JKEXCVBJDxKxGH8vRDz19W5rH0Egn6vajO28TTk7
KcuNxhHQmz8325K/Q94fDmK5ugI6h6vBXFwvN8rzwD4r6iQb7zpv9U48hyXFMZ02
oXQJDX1VoZ4Z53yuDQBAq1LAa4gPuDI=
X-Virus-Scanned: amavisd-new at mail.mydomain.com
X-Spam-Flag: NO
X-Spam-Score: -1
X-Spam-Level:
X-Spam-Status: No, score=-1 tagged_above=-100 required=6.2
tests=[ALL_TRUSTED=-1] autolearn=ham
Received: from mail.mydomain.com ([127.0.0.1])
by mail.mydomain.com (mail.mydomain.com [127.0.0.1]) (amavisd-new, port 10026)
with ESMTP id TCgEXrsa5S1c for <user@gmail.com>;
Thu, 10 Mar 2016 01:26:20 +0000 (UTC)
Received: from [192.168.1.2] (unknown [110.88.122.62])
by mail.mydomain.com (Postfix) with ESMTPSA id 0729341C5
for <user@gmail.com>; Thu, 10 Mar 2016 01:26:19 +0000 (UTC)
Content-Type: text/plain; charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 9.2 (3112))
Subject: Re: test
From: Zhang Huangbin <zhb@mydomain.com>
In-Reply-To: <CAJzwPONLqCNx32fs3_eDwBjqtk0mePa-cxvXzeQ2=-ATczkPKg@mail.gmail.com>
Date: Thu, 10 Mar 2016 09:26:09 +0800
Content-Transfer-Encoding: 7bit
Message-Id: <3A6C156F-ED37-4CE3-A2DB-5CBF839C4E1E@mydomain.com>
References: <20160310012216.5374035.64004.1304@mydomain.com> <CAJzwPONLqCNx32fs3_eDwBjqtk0mePa-cxvXzeQ2=-ATczkPKg@mail.gmail.com>
To: Zhang Huangbin <user@gmail.com>
X-Mailer: Apple Mail (2.3112)

MIME-Version: 1.0
Received: by 10.107.157.68 with HTTP; Wed, 9 Mar 2016 17:26:46 -0800 (PST)
In-Reply-To: <3A6C156F-ED37-4CE3-A2DB-5CBF839C4E1E@mydomain.com>
References: <20160310012216.5374035.64004.1304@mydomain.com>
<CAJzwPONLqCNx32fs3_eDwBjqtk0mePa-cxvXzeQ2=-ATczkPKg@mail.gmail.com>
<3A6C156F-ED37-4CE3-A2DB-5CBF839C4E1E@mydomain.com>
Date: Thu, 10 Mar 2016 09:26:46 +0800
Delivered-To: user@gmail.com
Message-ID: <CAJzwPOPWF6sy1xLc6S8bh4ru4f32WE8EJvomi0g6QKivkRg31A@mail.gmail.com>
Subject: Re: test
From: Zhang Huangbin <user@gmail.com>
To: Zhang Huangbin <zhb@mydomain.com>
Content-Type: text/plain; charset=UTF-8

Is it a BB10 issue/bug, or a SOGo issue?

Email sent from SOGo web UI contains 'In-Reply-To:', but no 'References:'.

When you reply from bb10 to gmail do you see a Cmd=SmartReply in sogo.log?
If a email is set via Cmd=SendMail sogo can only use the headers which are included in the email. With Cmd=SmartReply we pull the in-reply-to and references from the original mail.

I think that I've found the root cause of the issue.
References: mail header modified by SoGo, so some of the mail ids are splitted by new line character.

Example:

References: <m-id1@dom.tld><m-id2@dom.tld><m-id3@dom.tld>
<m-id4@dom.tld>

Should be:

References: <m-id1@dom.tld><m-id2@dom.tld><m-id3@dom.tld><m-id4@dom.tld>

I've tested everything by the following way:

send emails and replies until mail thread breaks on my BB. Then, I've just modified mail files directly on the server, so all References: headers became oneliners. And my BB started to show threads correctly.

Seems like BB IMAP\POP3 client behaves differently, only BB ActiveSync client have such problem with multiline References: header.

When you reply from bb10 to gmail do you see a Cmd=SmartReply in sogo.log?

I got "Cmd=SmartReply". So looks like SOGo diesn't add/update "References:" header.

Also, when I've checked EAS debug with working headers and without I found the following:

Multiple lines(breaking thread):

ConversationId of each mail contains BASE64 text of exact References list.

Single lines(working thread):
And it has some empty EAS command.

ConversationId of each email contains BASE64 text of only the first emails mail-id.

Example debug:

Working:

<To xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></To>
<From xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></From>
<Subject xmlns="Email:">Re: 1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:48:04.000Z</DateReceived>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT4=</ConversationId>

<To xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></To>
<From xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></From>
<Subject xmlns="Email:">Re: 1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:45:41.000Z</DateReceived>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT4=</ConversationId>

<To xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></To>
<From xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></From>
<Subject xmlns="Email:">Re: 1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:48:04.000Z</DateReceived>
<DisplayTo xmlns="Email:">alex.m</DisplayTo>
<Importance xmlns="Email:">1</Importance>
<Read xmlns="Email:">1</Read>
<MessageClass xmlns="Email:">IPM.Note</MessageClass>
<ContentClass xmlns="Email:">urn:content-classes:message</ContentClass>
<InternetCPID xmlns="Email:">65001</InternetCPID>
<Body xmlns="AirSyncBase:">
<Type>2</Type>
<Truncated>0</Truncated>
<Preview/>
<Data/>
<EstimatedDataSize>0</EstimatedDataSize>
</Body>
<Flag xmlns="Email:">
<FlagStatus>0</FlagStatus>
</Flag>
<Categories xmlns="Email:"/>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT4=</ConversationId>
<NativeBodyType xmlns="AirSyncBase:">2</NativeBodyType>

<To xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></To>
<From xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></From>
<Subject xmlns="Email:">1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:43:14.000Z</DateReceived>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT4=</ConversationId>

Not Working:

<To xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></To>
<From xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></From>
<Subject xmlns="Email:">Re: 1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:48:04.000Z</DateReceived>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT48MjAxNjAzMTAwODQ1NDEuNTEyNDE3Ni4xOTk
1OC4xNTUxQHlvdXJpdGNyb3dkLmNvbT4=</ConversationId>

<To xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></To>
<From xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></From>
<Subject xmlns="Email:">Re: 1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:45:41.000Z</DateReceived>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT4=</ConversationId>

<To xmlns="Email:">"Alexander Magliovany" <secondemail@youritcrowd.com></To>
<From xmlns="Email:">"Alexander Kalashnikov" <firstemail@yandex.ru></From>
<Subject xmlns="Email:">1111</Subject>
<ThreadTopic xmlns="Email:">1111</ThreadTopic>
<DateReceived xmlns="Email:">2016-03-10T08:43:14.000Z</DateReceived>
<ConversationId xmlns="Email2:">PDIwMTYwMzEwMDg0MzE0LjUxMjQxNzYuOTg0NTEuODM3QHlhbmRleC5ydT4=</ConversationId>

--
Should not this ConversationId be the same for a thread?

I've found exact place where the problem is.

Accorting to https://tools.ietf.org/html/rfc822#section-3.2 field-body can be "folded" as it stated in https://www.w3.org/Protocols/rfc822/3_Lexical.html
So, the code in ActiveSync/SOGoMailObject+ActiveSync.m too simple, because it will generate different ConversationID for "folded" References headers:

if ([reference length] > 0)
[s appendFormat: @"<ConversationId xmlns=\"Email2:\">%@</ConversationId>", [[reference dataUsingEncoding: NSUTF8StringEncoding] activeSyncRepresentationInContext: context]];
else if ([[self inReplyTo] length] > 0)
[s appendFormat: @"<ConversationId xmlns=\"Email2:\">%@</ConversationId>", [[[self inReplyTo] dataUsingEncoding: NSUTF8StringEncoding] activeSyncRepresentationInContext: context]];
else if ([[self messageId] length] > 0)
[s appendFormat: @"<ConversationId xmlns=\"Email2:\">%@</ConversationId>", [[[self messageId] dataUsingEncoding: NSUTF8StringEncoding] activeSyncRepresentationInContext: context]];

I think the problem is caused by sope. While unfolding header fields sope consumes the cr and whitespace instead of only the whitespace.

So, how to fix this?

I sent a patch for review to Ludovic.

Thank you.

Also, please, consider the following situation:

references: <5693EB11.2020703@youritcrowd.com><EEA40A16E7B7C240B0769E7126EA9DF013A93E7B@XMB102FCNC.rim.net>

When references includes m-ids without spaces.

Yes, this is exactly the problem I described above.

If I've understood you correctly, then the following headers in the mail will be parsed correctly after the patch?

references: <5693EB11.2020703@youritcrowd.com><EEA40A16E7B7C240B0769E7126EA9DF013A93E7B@XMB102FCNC.rim.net>

references: <5693EB11.2020703@youritcrowd.com> <EEA40A16E7B7C240B0769E7126EA9DF013A93E7B@XMB102FCNC.rim.net>

references: <5693EB11.2020703@youritcrowd.com>
EEA40A16E7B7C240B0769E7126EA9DF013A93E7B@XMB102FCNC.rim.net>

I'm not sure i understand @st41ker's comment. but "References:" should be allowed to contain multiple message-ids separated by space. Even the RFC document shows the example with multiple message-id this way (search the last "References:" in below rfc document):
http://www.ietf.org/rfc/rfc2822.txt

References: <1234@local.machine.example> <3456@example.net>

If you check other MUAs, some of they generate "References:" this way too, and it works fine. e.g. Mac Mail.app. And Gmail has one message-id per line.

@zhb.

RFC2822
3.6.4. Identification fields
The "References:" and "In-Reply-To:" field each contain one or more
unique message identifiers, optionally separated by CFWS.

@tfu
Could you, please, provide me the patch also, so I could test it?

Dear developers,

Any update on this issue?