Name | Description contents and Locations | Migrate? |
*.pst | Personal Message Store
Main
data file for Outlook containing all you Mail, Calendar, Contacts,
Tasks, Notes and Journal items. In addition to that it can contain
"hidden" data or settings such as Views, Rules, Categories (since
Outlook 2007), per folder AutoArchive settings, etc…
By default
the first pst-file is called outlook.pst. When you have AutoArchive
enabled, you’ll have a file called archive.pst as well.
If you
connect to a SharePoint List, then you’ll also have a file called
"SharePoint Lists.pst". IMAP accounts also uses this file format to
cache their data in.
Additional automatically created pst-files
are appended with a number e.g.; outlook0,pst, outlook1.pst,
archive0.pst, etc…
You can create additional pst-files if you want and can place them in a different location but network locations are not supported.
Further information about the pst-file can be found here.
Corruption of the main pst-file can prevent Outlook from loading correctly and could also lead to data loss. Therefore you should backup these files on a regular basis. | Possible |
Location: Local Profile Settings |
*.ost | Offline Message Store
Similar
to a pst-file but represents an offline cache of an on-line mailbox
intended to enable offline access and to reduce network traffic or to
increase Outlook performance when using a slow connection. These files
were originally used only to cache an Exchange mailbox but the Outlook Connector also uses this file format to cache Live Hotmail mailboxes.
By
default the file is called outlook.ost when connecting to Exchange and
<Live ID>.ost when created by the Outlook Connector e.g.;
yourname_hotmail.ost or yourname_live.ost.
Additional automatically created ost-files are appended with a number e.g.; outlook0.ost, outlook1.ost
As
it is merely a cache and the actual data remains on the server, there
is no need to backup this file. When it gets corrupted it can prevent Outlook from loading correctly but as long as you still have access to the Exchange server
you can recover by renaming it to .old. Upon deletion (or renaming) it
will be automatically recreated when you connect to the mail server
again. | Not needed |
Location: Local Profile Settings |
*.nst | Notes Message Store
Similar
to an ost-file but then used for an offline cache for use by Lotus
Notes Connector accounts. It may also be used by other connector type
accounts. Older versions of the Outlook Connector for instance also
have used this file format. | Not needed |
Location: Local Profile Settings |
*.pst.tmp | A temporary file indicating a file lock on or queued data to be written to the similarly named pst-file. | Not needed |
Location: Local Profile Settings |
*.ost.tmp | A temporary file indicating a file lock on or queued data to be written to the similarly named ost-file. | Not needed |
Location: Local Profile Settings |
*.oab | Offline Address Book files for Exchange accounts.
It
consist out of 6 files all containing different information or indexes
about the users in the corporate global address book (GAL). Similar to
the ost-file it is designed for offline usage, reducing network traffic
and optimizing responsiveness when working on a slow connection. | Not needed |
Location: Local Profile Settings |
*.oft | Outlook Form Template
Templates and custom forms are stored in the oft-format when saved outside of Outlook.
You should make a backup of these files and you can also migrate them for use on another computer. | Possible |
Location: Templates |
*.xnk | Exchange Shortcuts
These
files represent shortcut links to folders accessible within Outlook.
They are similar to computer shortcuts (lnk-files) which point to other
files on the computer.
Since Outlook 2007 the file format is no longer registered for direct execution but that can be enabled again.
You
can migrate these files to another computer or even share them (when
they link to a Public Folder for instance) but of course that location
should also be available on the other computer. | Possible |
Location: Folder of choice |
*.pab | This is the Personal Address Book file.
Previous
versions of Outlook allowed you to store your contacts in a pab-file if
you didn’t use the Contact folder. The main reason for having a
pab-file was that the Contacts folder in Outlook 97/98 didn’t support
personal distribution lists. This feature was added in Outlook 2000. In
Outlook XP/2002 a pab-file was no longer created or linked by default
but could be manually added. Since Outlook 2007 you can only directly
import pab-files into your Contacts folder.
If you still use
pab-files for some reason, you should either back it up or import them
into the Contacts folder and stop using them completely. | Possible/
not needed |
Location: Roaming Profile Settings |
*.rwz | Outlook Rules Wizard
This
file format can store your rules that you have configured in Outlook.
Since Outlook XP/2002, rules are stored within the mailbox itself
instead of a separate file. You can still create a backup of your rules in the rwz-format and import them.
You
can make a backup of this file for local use when you still use Outlook
2000 or previous but due to in-file dependencies you shouldn’t attempt
to migrate this file. | Not possible/
not needed |
Location: Roaming Profile Settings |
*.qat | Contains the Quick Access
Toolbar (QAT) configuration information. There are up to 19 qat-files
for Outlook 2007. For an overview of their naming and which type of
window they apply to see this post. | Possible |
Location: Local Profile Settings |
*.msg | Outlook uses the msg-format to
store messages and other mailbox items outside of Outlook without
losing the Outlook interface when you open them from outside of
Outlook. Any attachments that the message holds are also contained
within this file. This allows you to open individual items on another
computer on which Outlook is installed. Note that msg-files created in the Unicode format cannot be opened in Outlook XP/2002 or previous. | Possible |
Location: Folder of Choice |
*.htm
*.txt
*.rtf | Outlook uses these "well known
formats" to store the signatures in or to store Outlook messages in a
format which can be used by other applications as well.
In case of
the signatures, additional files and folders can be created in the
signatures folder to save formatting information or pictures which have
been used in the signature.
When saving a message in this format, attachments will not be saved with it. | Possible |
Location: Signatures
Location: Folder of choice (when saving messages) |
*.mlog | Log file created by the Outlook Connector mainly for use of handling meeting requests correctly.
This file is automatically created or recreated when missing upon starting Outlook. | Not needed |
Location: Local Profile Settings |
*.otm
vbaproject.otm | Outlook VBA Module
Contains
your configured macros and VBA programs created in the Visual Basic
Editor. The default first project is stored in a file vbaproject.otm.
If you have any macros configured, it is highly recommended to make a
backup of this file or document your code elsewhere. You can also
migrate these files to another computer. | Possible |
Location: Roaming Profile Settings |
outcmd.dat | Outlook Commands
This file contains the command bar and menu customizations that you make in Outlook. is corrupted, it can prevent Outlook from loading correctly.
You
can make a backup of this file for local use but due to dependencies of
installed addins, it is not recommended to migrate this file between
computers. It is worth a shot to try it though as in case you run into
issues, you simply rename the file to outcmd.old to reset. | Not recommended |
Location: Roaming Profile Settings |
extend.dat | This file contains information and settings for registered Exchange Client Extensions (ECE).
When it is corrupted, it can prevent Outlook from loading correctly.
There
is no need to make a backup of this file. Upon deletion it is
automatically recreated from registry information. You shouldn’t
migrate this file between computers as there is no need to do so since
it is recreated from information on the local computer. When migrating,
you’ll likely end up corrupting the configuration. | Not needed |
Local: Local Profile Settings |
views.dat | Contains view settings for displaying of the folders.
This
file is used by Outlook XP/2002 and previous and no longer used by
later versions of Outlook as since Outlook 2003 this information is
contained in the mailbox or pst-file.
You can make a backup of
this file for local use when you still use Outlook XP/2002 or previous
but due to in-file dependencies you shouldn’t attempt to migrate this
file. | Not possible |
Location: Roaming Profile Settings |
frmcache.dat | Forms Cache
A cache
file holding information about the cached custom forms in the local
Forms folder. If it gets corrupted, custom forms might prevent from
loading, display older versions of the form or my cause other
unexpected results. Recovering can be achieved by clearing the folder which can be done in several ways. | Not needed |
Location: Forms Local Cache |
Normail.dot | Normal.dot is the default file
Word 2003 and previous use to store settings such as formatting styles,
AutoText, custom toolbars and macros.
When you use Word as your
email editor, in Outlook 2003 or previous, then this file gets loaded
as well. It is also used when you have Word set as your default HTML
editor and use the "Advanced Editor" to create a signature.
If the
normal.dot file gets corrupted or if certain addins or ActiveX
components are installed in Word, this will affect Outlook’s behavior
as well. Resetting the normal.dot file can be done by renaming it to
.old.
This file should be backed up if you made custom changes and
the file can be migrated between machines although certain addin
dependencies can prevent it from working correctly. | Possible |
Location: Templates |
NormalEmail.dotm | NormalEmail.dotm is similar to
the normal.dot file and has been introduced in Outlook 2007 to support
the new email editor and to break the dependencies with Word and to
offer Outlook specific support. Quick Parts information is also stored in this file.
This file should be backed up if you made custom changes and the file can be migrated between machines. | Possible |
Location: Templates |
custom.dic | TThis file contains the words
which you add to the dictionary via the spell check options. Since
Outlook 2007 it is stored in the Unicode format and its location
changed from the Proof folder to the UProof folder.
This is a shared file between other Office applications. The file can be edited via the spell check options in the Office applications that use it or directly via Notepad.
This file should be backed up if you made custom changes and the file can be migrated between machines. | Possible |
Location: Proof (Outlook 2003 and previous)
Location: UProof (Since Outlook 2007) |
offitems.log
outitems.log | These files contain items that have been added to the Journal or should still be added to the Journal.
When
all the latest changes have been committed to the mailbox, then you can
safely remove these files without losing data.
The file
outitems.log tracks Outlook items that have been created during the
last Outlook session and the file offitems.log tracks documents created
by other Office applications which have been committed to Outlook
during the last Outlook session or should still be committed when
Outlook is closed. | Not needed |
Location: Roaming Profile Settings |
RefEdit.exd | A cache of used form controls to speed up inserting the control again at a later time. | Not needed |
Location: Forms Roaming |
outlook.box | Contains settings for the custom Toolbox when designing a form. | Not recommended |
Location: Forms Roaming |
<profilename>.nk2 | Outlook AutoSuggest file (sometimes also named "AutoComplete file" or "nickname cache")
This
file is used in Outlook 2002/XP, Outlook 2003 and Outlook 2007 to cache
up to 1000 addresses that have been used before to address an email,
meeting request, task request, etc…
This file holds no relation to the Contacts folder and shouldn’t be relied on to securely save contact information as it is only a cache. You should really use the Contacts folder for that.
If
you like to keep the cached information, you can migrate this file
between machines as long as you rename the file after the name of the
mail profile and the version of Outlook is the same. However,
corruption of the file could break the mail profile or vice versa. In
that case the mail profile should be recreated. | Possible |
Location: Roaming Profile Settings |
<profilename>.nick | Same as above but then used in Outlook 2000. | Possible |
Location: Roaming Profile Settings |
<profilename>.fav | This file is used in Outlook
2002/XP and previous to hold the configured shortcuts (Favorites) in
the Outlook Bar for the corresponding mail profile. The Outlook Bar has
been replaced by the Navigation Pane in Outlook 2003 and later (see
<profilename.xml>). | Possible |
Location: Roaming Profile Settings |
<profilename>.srs | This file holds the send/receive settings for the corresponding mail profile.
You can make a backup of this file for local use but due to in-file dependencies you shouldn’t attempt to migrate this file. | Not possible |
Location: Roaming Profile Settings |
<profilename>.xml | This file holds customization
settings for the Navigation Pane in Outlook 2003 and later. Most
notable settings are, Favorite Folders, Shortcuts from the Shortcuts
Navigation and opened shared folder lists in the Calendar, Contacts,
Tasks and Notes and Journal Navigation.
A corruption of the file can lead to loss of these configuration settings, being unable to
remove certain folders or wrong folders showing up in the described
sections.
You can make a backup of this file for local use but due to in-file dependencies you shouldn’t attempt to migrate this file. | Not possible |
Location: Roaming Profile Settings |
<profilename>.sharing.xml.obi
~last~.sharing.xml.obi | Contains information about the
last sync process of (shared) services subscriptions such as RSS feeds,
Exchange, SharePoint and Internet Calendar.
~last~.sharing.xml.obi contains the latest sync information of RSS feeds with Internet Explorer (Common Feed List). | Not needed |
Location: Local Profile Settings |
<profilename>.xml.klf | Known Feed List.
This
files contains information about which RSS feeds the specified Outlook
mail profile syncs with the Common Feed List feature of Internet
Explorer. | Not needed |
Location: Local Profile Settings |
OutlPrnt | This file contains the print style settings.
When
it gets corrupted or if it becomes very large (in general, even with a
lot of custom printing styles, this file shouldn’t be larger than a
couple of hundred KB in size), you could run into printing errors.
Rename it or delete it to recover. | Possible |
Location: Roaming Profile Settings |