I will start by describing the problem..

I had an email account configured in Outlook 2010 connected to an Exchange server. I backed up my emails locally into a PST file. (now I no longer have access to the Exchange account)

Next I wanted to export these archived mails to be used inside Thunderbird 10.x (place them in the Local Folders in TB). The PST file is around 500MB in size.

I tried different methods:

  • My first attempt was to use the Import > Mail > Outlook feature directly from inside TB as suggested here.
  • In another attempt, I "copied" my emails (drag-drop) to a third common IMAP email configured in both Outlook and Thunderbird (which is in fact a locally running mail server on the interface), then I pulled them into my local folder once inside TB.
  • I even tried to use Outlook Express as an intermediary step (Outlook -> Outlook Express -> Thunderbird).

All the above fails, as the emails are not preserved when exported. I have encountered a number of problems, to name a few:

  • if we have Content-Type: multipart/alternative; emails with both html/text formats, then only the html one is exported.
  • different encodings are sometimes used than the original ones (base64, quoted-printable, etc..)
  • the history of routes (Received: headers) is completely gone
  • the addresses are sometimes lost and simply the display name is kept. ex: To: "First Last" <nick@server.com> gets transformed into: To: "First Last"
  • sometimes the whole sender/receiver address is lost, and simply duplicated from the opposite field
  • the date field timezone gets changed to the current machine's timezone (not a biggie)
  • all sorts of other headers are added/removed/rewritten differently...

So my question is how can I export emails from my PST file into Thunderbird's EML/MBOX textual format, in a clean way the preserves all the original headers?

I understand that the specification of PST files is now publicly available (right?), so I'm hoping someone developed a decent tool for this task.. The way I see it, if we somehow had access to the raw emails in Outlook (like view-source in TB), it shouldn't be hard to simply write them to text files!!

BTW: In Outlook Express we could directly choose File > Save As and export in .eml format, but Outlook 2010 only have the (proprietary?) binary .msg format option (or am I missing something)...

Here's a sample to show how the emails get mangled -- names and other stuff have been changed to protect the innocent :)

Original email in Outlook (open email in new window, go to File > Properties and inspect the 'Internet headers' text field, although sometimes its just blank!)

Received: from mail.server (
 by s2.server ( with Microsoft SMTP Server id 14.0.702.0; 
 Thu, 3 Feb 2011 12:51:26 -0500
Received: from mail.server (mail.server [])
 by mail.server (8.14.5.Beta0/8.14.5.Beta0) with ESMTP id p00000000000002;
 Thu, 3 Feb 2011 12:51:26 -0500
Received: from smtp.server (smtp.server [])
 by mail.server (8.14.5.Beta0/8.14.5.Beta0) with ESMTP id p00000000000001
 for <list@server>; Thu, 3 Feb 2011 12:51:16 -0500
Received: from s3.server (s4.server [])
 by smtp.server (8.14.4/8.14.4) with ESMTP id p0000000000000
 for <list@server>; Thu, 3 Feb 2011 12:51:16 -0500 (envelope-from sender@server)
Received: from s1.server ([ffff::0000:000:0000:0000])
 by s3.server ([ffff::1111:000:0000:0000%12]) with mapi; 
 Thu, 3 Feb 2011 12:51:15 -0500
From: sender@server
Subject: test
Thread-Topic: test
Thread-Index: A0000000011112222333344445555g==
Date: Thu, 3 Feb 2011 12:51:15 -0500
Message-ID: <99887766554433221100FFEEDDCCBBAA99887766@s1.server>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
To: undisclosed-recipients:;
Return-Path: list-request@server
X-MS-Exchange-Organization-AuthSource: s2.server
X-MS-Exchange-Organization-AuthAs: Anonymous
X-MS-Exchange-Organization-AVStamp-Mailbox: MSFTFF;1;0;0 0 0
X-MS-Exchange-Organization-SCL: -1

Imported email into Thunderbird (simply Ctrl+U to view source)

From: sender@server
Subject: test
Thread-Index: A9999888877776666555544443333g==
Date: Thu, 3 Feb 2011 12:51:15 -0500
Message-ID: <99887766554433221100FFEEDDCCBBAA99887766@s1.server>
acceptlanguage: en-US
Content-Language: en-us
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
To: sender@server
X-Mailer: Microsoft Outlook 14.0
x-ms-exchange-organization-authsource: s2.server
x-ms-exchange-organization-authas: Anonymous
X-OlkEid: 00112233445566778899AABBCCDDEEFF00112233
  • There should be no problems in exporting emails from Outlok pst to Thunderbird. Are You sure that export from Exchange (ost) to simple pst went properly? Could You check it by exporting pst into clear Outlook profile? – Adam RichardSon Mar 3 '12 at 20:12
  • I never used it in that way, but I've found sth like this - it may help You. kb.mozillazine.org/Import_.pst_files – Adam RichardSon Mar 3 '12 at 20:15

The only tool that actually reconstructs headers is OutlookFreeware.com's Export Messages to EML Format utility. It's free and easy to use. I recommend it because I'm one of its developers.


The mozillaZine article Import .pst files treats the problem.

You need to have both Thunderbird and Outlook installed on the same computer, while Outlook is defined as the default email client, and then use Tools -> Import -> Mail within Thunderbird.

As you have already seen the above article, please let us know why it doesn't work for you.

You could also try the Thunderbird PST Import plugin.

  • Unfortunatenly this doesn't work when using a 64bit Outlook while TB is only 32 bit. – Devolus Dec 3 '14 at 16:22

Another option is to create a GMAIL account. Enable IMAP in your GMAIL account and then configure Outlook to use the IMAP GMAIL account. Copy your files from your PST to your IMAP GMAIL account inside Outlook. Then configure your Google IMAP account in Thunderbird and copy the files to your local storage.


The easiest solution I found was MailStore, free for home use:

You install it and backup your email as eml then you can import it into any email client.

protected by Community Sep 15 '16 at 11:22

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