.pst
Encyclopedia
In computing
, a Personal Storage Table (.pst) is an open proprietary file format used to store copies of messages, calendar events, and other items within Microsoft
software such as Microsoft Exchange Client
, Windows Messaging
, and Microsoft Outlook
. The open format is controlled by Microsoft who provide free specifications and free irrevocable technology licensing.
The file format is also known as:
, the messages, the calendar, and other data items are delivered to and stored on the server
. Microsoft Outlook
stores these items in a personal-storage-table (.pst) or off-line-storage-table (.ost) files that are located on the local computer. Most commonly, the .pst files are used to store archived items and the .ost files to maintain off-line availability of the items.
The size of these files no longer counts against the size of the mailbox used; by moving files from a server mailbox to .pst files, users can free storage space on their mailservers. To use the .pst files from another location the user needs to be able to access the files directly over a network from his mail client. While it is possible to open and use a .pst file from over a network, this is unsupported, and Microsoft advises against it, as .pst files are prone to corruption when used in this manner.
Both the .pst and .ost files use a fixed-block-based allocation scheme; the file is enlarged by a fixed amount of bytes, and the file internally maintains information about the allocated and non-allocated blocks. So, when data files like email messages are added to a .pst file, its file size is automatically adjusted by the mail client (if necessary). When mail is deleted from a .pst file, the size of the .pst file will stay the same, marking the space as unallocated so that it will hold future data items. Recently removed data items can actually be recovered from .pst and .ost files.
To reduce the size of .pst files, the user needs to compact them.
integer representation of itself
in the .pst file. Outlook checks to make sure that
it matches the user-specified password and refuses to operate if there is
no match. The data is readable by
the libpst project code.
Microsoft (MS) offers three values for the encryption setting: none,
compressible, and high.
Note that neither of the two encryption modes uses the user-specified password as any part of the key for the encryption.
, Windows Messaging
, and Microsoft Outlook
. The .pst file format is an open format for which Microsoft provides free specifications and irrevocable free patent licensing through the Open Specification Promise
The libpst project includes tools to convert .pst files into open formats such as mbox
and LDAP Data Interchange Format
. libpst is licensed under the GPL and is now included in Fedora 10. MVCOM is a commercially licensed COM Component that provides access to .pst files without MAPI.
As with any file, .pst files can become corrupted. Prior to Outlook 2003, the default .pst file format was ANSI and had a maximum size of 2 GB. If the .pst file were allowed to grow over 2 GB, the file would become unusable. Microsoft provides PST2GB a tool that can be used to truncate a .pst file that has grown over 2 GB. Microsoft also provides scanpst.exe, that can be used to repair other .pst file-corruption issues. In Outlook 2003 and later, .pst files are created in the Unicode format and have a default maximum size of 20 GB.
There are tools to convert .pst to other formats or to upload to other online e-mails like Gmail, for example.
(extended ASCII with a codepage) encoding for their .pst and .ost files. This format has a maximum size of 2 GB (231 bytes) and does not support unicode
. A file exceeding this size is likely to give error messages, such as ".pst has reached maximum size limit," and could become corrupted. Although superseded, this format continues to be supported by Microsoft Outlook 97 and later (98, 2000, 2002 (XP), 2003, 2007), by Internet Message Access Protocol Version 4rev1 (IMAP4) accounts and by HTTP accounts.
From Outlook 2003 and onward, the standard format for .pst and .ost files is Unicode
(UTF-16 little-endian). The use of 64-bit pointers instead of the 32-bit pointers of the earlier version allowed to overcome the 2 GB limit. Now, there is a user-definable maximum-file size up to 20 GB. This format is supported by Microsoft Outlook 2003 and later (2007) A file that is created in the personal-folders format in Outlook 2003 or in Microsoft Office Outlook 2007 is not compatible with earlier versions of Microsoft Outlook and cannot be opened by using those older versions.
If this limit is reached or sometimes exceeded, retrieval of the .pst file can be difficult if not impossible.
The file is structured as a B-tree
with 512 byte nodes and leafs.
is Microsoft's email and personal information program for Mac OS X
. While superficially similar to Outlook, it is an entirely different application, and uses a unique database format which cannot be imported or exported, though user data can be imported and exported to and from another unique format called .rge (a bundle consisting of many individual files plus metadata
). Entourage 2008, the current version as of May 2010, has no support for .pst files, though there exists Microsoft's .pst import tool for Entourage 2004; however, the tool could only import .pst files from Outlook for Mac 2001, and not any Windows versions. Entourage is being replaced by Outlook for Office 2011 for Intel Macs, which will be able to import Outlook .pst files from Windows; however, data will be stored as many individual files, rather than in a single database such as .pst or the Entourage database.
Outlook for Mac 2001, which runs under Mac OS 9 or the Mac OS X Classic Environment, connects exclusively to Exchange servers, and to this day is closer to its Windows counterpart than Entourage is. It works directly with 'Outlook 97-2002' .pst files, and can freely interchange those files with Outlook for Windows, as recent versions are still compatible with the older .pst format.
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, a Personal Storage Table (.pst) is an open proprietary file format used to store copies of messages, calendar events, and other items within Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
software such as Microsoft Exchange Client
Microsoft Exchange Client
Microsoft Exchange Client was a multi-purpose messaging product useful for managing e-mail. It was the native and bundled client for Microsoft Exchange Server up to version 5.0, later superseded by Microsoft Outlook....
, Windows Messaging
Windows Messaging
Windows Messaging, initially called Microsoft Exchange, is an e-mail client that was included with Windows 95 , 98 and Windows NT 4.0.In Windows 98, it is not installed by default, but available as a separate program in the setup CD....
, and Microsoft Outlook
Microsoft Outlook
Microsoft Outlook is a personal information manager from Microsoft, available both as a separate application as well as a part of the Microsoft Office suite...
. The open format is controlled by Microsoft who provide free specifications and free irrevocable technology licensing.
The file format is also known as:
- Personal Folder File
- Off-line Storage Table (.ost)
- Off-line Folder File
- Personal Address Book (.pab)
Overview
In Microsoft Exchange ServerMicrosoft Exchange Server
Microsoft Exchange Server is the server side of a client–server, collaborative application product developed by Microsoft. It is part of the Microsoft Servers line of server products and is used by enterprises using Microsoft infrastructure products...
, the messages, the calendar, and other data items are delivered to and stored on the server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
. Microsoft Outlook
Microsoft Outlook
Microsoft Outlook is a personal information manager from Microsoft, available both as a separate application as well as a part of the Microsoft Office suite...
stores these items in a personal-storage-table (.pst) or off-line-storage-table (.ost) files that are located on the local computer. Most commonly, the .pst files are used to store archived items and the .ost files to maintain off-line availability of the items.
The size of these files no longer counts against the size of the mailbox used; by moving files from a server mailbox to .pst files, users can free storage space on their mailservers. To use the .pst files from another location the user needs to be able to access the files directly over a network from his mail client. While it is possible to open and use a .pst file from over a network, this is unsupported, and Microsoft advises against it, as .pst files are prone to corruption when used in this manner.
Both the .pst and .ost files use a fixed-block-based allocation scheme; the file is enlarged by a fixed amount of bytes, and the file internally maintains information about the allocated and non-allocated blocks. So, when data files like email messages are added to a .pst file, its file size is automatically adjusted by the mail client (if necessary). When mail is deleted from a .pst file, the size of the .pst file will stay the same, marking the space as unallocated so that it will hold future data items. Recently removed data items can actually be recovered from .pst and .ost files.
To reduce the size of .pst files, the user needs to compact them.
Data access
Password protection can be used to protect the content of the .pst files. However, Microsoft admits that the password adds very little protection, due to the existence of commonly available tools which can remove or simply bypass the password protection. The password to access the table is stored without the first and last XOR CRC-32Cyclic redundancy check
A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
integer representation of itself
in the .pst file. Outlook checks to make sure that
it matches the user-specified password and refuses to operate if there is
no match. The data is readable by
the libpst project code.
Microsoft (MS) offers three values for the encryption setting: none,
compressible, and high.
- None the .pst data is stored as plain text.
- Compressible the .pst data is encrypted with a byte-substitution cipherCipherIn cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...
with a fixed substitution table. - High (sometimes called "better") encryption is similar to a WWII German Enigma cipher with three fixed rotors.
Note that neither of the two encryption modes uses the user-specified password as any part of the key for the encryption.
Support
The .pst file format is supported by several Microsoft client applications, including Microsoft Exchange ClientMicrosoft Exchange Client
Microsoft Exchange Client was a multi-purpose messaging product useful for managing e-mail. It was the native and bundled client for Microsoft Exchange Server up to version 5.0, later superseded by Microsoft Outlook....
, Windows Messaging
Windows Messaging
Windows Messaging, initially called Microsoft Exchange, is an e-mail client that was included with Windows 95 , 98 and Windows NT 4.0.In Windows 98, it is not installed by default, but available as a separate program in the setup CD....
, and Microsoft Outlook
Microsoft Outlook
Microsoft Outlook is a personal information manager from Microsoft, available both as a separate application as well as a part of the Microsoft Office suite...
. The .pst file format is an open format for which Microsoft provides free specifications and irrevocable free patent licensing through the Open Specification Promise
Microsoft Open Specification Promise
The Microsoft Open Specification Promise , is a promise by Microsoft, published in September 2006, to not assert legal rights over certain Microsoft patents on implementations of an included list of technologies....
The libpst project includes tools to convert .pst files into open formats such as mbox
Mbox
mbox is a generic term for a family of related file formats used for holding collections of electronic mail messages. All messages in an mbox mailbox are concatenated and stored as plain text in a single file...
and LDAP Data Interchange Format
LDAP Data Interchange Format
The LDAP Data Interchange Format is a standard plain text data interchange format for representing LDAP directory content and update requests. LDIF conveys directory content as a set of records, one record for each object...
. libpst is licensed under the GPL and is now included in Fedora 10. MVCOM is a commercially licensed COM Component that provides access to .pst files without MAPI.
As with any file, .pst files can become corrupted. Prior to Outlook 2003, the default .pst file format was ANSI and had a maximum size of 2 GB. If the .pst file were allowed to grow over 2 GB, the file would become unusable. Microsoft provides PST2GB a tool that can be used to truncate a .pst file that has grown over 2 GB. Microsoft also provides scanpst.exe, that can be used to repair other .pst file-corruption issues. In Outlook 2003 and later, .pst files are created in the Unicode format and have a default maximum size of 20 GB.
There are tools to convert .pst to other formats or to upload to other online e-mails like Gmail, for example.
Size and formats
Outlook 2002 and earlier use ANSIWindows code page
Windows code pages are sets of characters or code pages used in Microsoft Windows from the 1980s and 1990s...
(extended ASCII with a codepage) encoding for their .pst and .ost files. This format has a maximum size of 2 GB (231 bytes) and does not support unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
. A file exceeding this size is likely to give error messages, such as ".pst has reached maximum size limit," and could become corrupted. Although superseded, this format continues to be supported by Microsoft Outlook 97 and later (98, 2000, 2002 (XP), 2003, 2007), by Internet Message Access Protocol Version 4rev1 (IMAP4) accounts and by HTTP accounts.
From Outlook 2003 and onward, the standard format for .pst and .ost files is Unicode
Unicode
Unicode is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems...
(UTF-16 little-endian). The use of 64-bit pointers instead of the 32-bit pointers of the earlier version allowed to overcome the 2 GB limit. Now, there is a user-definable maximum-file size up to 20 GB. This format is supported by Microsoft Outlook 2003 and later (2007) A file that is created in the personal-folders format in Outlook 2003 or in Microsoft Office Outlook 2007 is not compatible with earlier versions of Microsoft Outlook and cannot be opened by using those older versions.
If this limit is reached or sometimes exceeded, retrieval of the .pst file can be difficult if not impossible.
The file is structured as a B-tree
B-tree
In computer science, a B-tree is a tree data structure that keeps data sorted and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree is a generalization of a binary search tree in that a node can have more than two children...
with 512 byte nodes and leafs.
Entourage and Outlook for Mac
Microsoft EntourageMicrosoft Entourage
Microsoft Entourage was an e-mail client and personal information manager developed by Microsoft for Mac OS 8.5 and higher. Microsoft first released Entourage in October 2000 as part of the Microsoft Office 2001 office suite; Office 98, the previous version of Microsoft Office for Mac OS included...
is Microsoft's email and personal information program for Mac OS X
Mac OS X
Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...
. While superficially similar to Outlook, it is an entirely different application, and uses a unique database format which cannot be imported or exported, though user data can be imported and exported to and from another unique format called .rge (a bundle consisting of many individual files plus metadata
Metadata
The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...
). Entourage 2008, the current version as of May 2010, has no support for .pst files, though there exists Microsoft's .pst import tool for Entourage 2004; however, the tool could only import .pst files from Outlook for Mac 2001, and not any Windows versions. Entourage is being replaced by Outlook for Office 2011 for Intel Macs, which will be able to import Outlook .pst files from Windows; however, data will be stored as many individual files, rather than in a single database such as .pst or the Entourage database.
Outlook for Mac 2001, which runs under Mac OS 9 or the Mac OS X Classic Environment, connects exclusively to Exchange servers, and to this day is closer to its Windows counterpart than Entourage is. It works directly with 'Outlook 97-2002' .pst files, and can freely interchange those files with Outlook for Windows, as recent versions are still compatible with the older .pst format.
External links
- Microsoft has released some of the format specification and reference implementation.
- You can convert the OST file in to PST file by and learn tricks about Microsoft Outlook .pst file
- libpst project: format of Microsoft Outlook .pst file
- libpst project - contains many utilities to convert .pst files to other mailbox formats
- A great deal of information about the format has been documented by the libpff project, including some of the Personal Folder File format specifications and MAPI definitions.