Personal Storage Table

Last updated

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.

Contents

The file format may also be known as a Personal Folders (File) or Post Office File. When functioning in its capacity as a cache for Outlook's Cached Exchange Mode feature, it may be called an Off-line Storage Table (.ost) or an Off-line Folders (File). [1]

Overview

In Microsoft Exchange Server, 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. This is an essential feature of Microsoft Outlook.

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. [2] To use the .pst files from another location the user needs to be able to access the files directly over a network from their 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. [3]

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. [4]

Data access

Password protection can be used to protect the content of the .pst files. [5] 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. [6] The password to access the table is stored without the first and last XOR CRC-32 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.

Support

The .pst file format is supported by several Microsoft client applications, including Microsoft Exchange Client, Windows Messaging, and Microsoft Outlook; in the previous two, it was often used with a Personal Address Book (.pab) file, which stores address book. The .pst file format is an open format for which Microsoft provides free specifications and irrevocable free patent licensing through the Open Specification Promise. [7]

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.

There are tools to convert .pst to other formats or to upload to other online e-mails like Gmail, for example. [8]

Formats and size

The file is structured as a B-tree with 512 byte nodes and leaves. [9] All PST files begin with the four-byte magic string "!BDN", a four-byte CRC number, and a two-byte magic string of "SM". [10]

Outlook 2002 and earlier use ANSI (extended ASCII with a codepage) encoding for their .pst and .ost files. This format has a maximum size of 2 GiB (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 is supported by all Outlook versions, by Internet Message Access Protocol Version 4rev1 (IMAP4) accounts and by HTTP accounts. [11]

From Outlook 2003 and onward, the new standard format for .pst and .ost files is Unicode (UTF-16 little-endian), with 64-bit pointers instead of 32-bit to allow larger than 2 GiB sizes. The limit became 20 GB for Outlook 2003-2007, and increased to 50 GB from Outlook 2010. [12] [11] [13] A file that is created in the personal-folders format in Outlook 2003 or later is not compatible and cannot be opened by earlier versions. [2]

As with any file, .pst files can become corrupted. Growth over the limit has been a consistent problem; ANSI .pst that grew beyond 2 GiB and Unicode .pst that grew beyond 20 or 50 GB would become unusable. The scanpst.exe tool has been included with all versions of Outlook to detect and repair .pst database corruption, and Microsoft at one point offered a special-purpose PST2GB that would simply truncate the file to 2 GiB to allow Outlook to repair it.

Entourage and Outlook for Mac

Microsoft Entourage was Microsoft's email and personal information program for Mac OS X (replaced by Outlook for Macintosh in Microsoft Office for Mac 2011). While superficially similar to Outlook, it was an entirely different application, and used 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's replacement, Outlook for Office 2011 for Intel Macs, was able to import Outlook .pst files from Windows; [14] 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. The limit for Outlook 2011 is 10GB.

Related Research Articles

<span class="mw-page-title-main">Microsoft Office</span> Suite of office software

Microsoft Office, or simply Office, is a family of client software, server software, and services developed by Microsoft. It was first announced by Bill Gates on August 1, 1988, at COMDEX in Las Vegas. Initially a marketing term for an office suite, the first version of Office contained Microsoft Word, Microsoft Excel, and Microsoft PowerPoint. Over the years, Office applications have grown substantially closer with shared features such as a common spell checker, Object Linking and Embedding data integration and Visual Basic for Applications scripting language. Microsoft also positions Office as a development platform for line-of-business software under the Office Business Applications brand.

New Technology File System (NTFS) is a proprietary journaling file system developed by Microsoft. Starting with Windows NT 3.1, it is the default file system of the Windows NT family. It superseded File Allocation Table (FAT) as the preferred filesystem on Windows and is supported in Linux and BSD as well. NTFS reading and writing support is provided using a free and open-source kernel implementation known as NTFS3 in Linux and the NTFS-3G driver in BSD. By using the convert command, Windows can convert FAT32/16/12 into NTFS without the need to rewrite all files. NTFS uses several files typically hidden from the user to store metadata about other files stored on the drive which can help improve speed and performance when reading data. Unlike FAT and High Performance File System (HPFS), NTFS supports access control lists (ACLs), filesystem encryption, transparent compression, sparse files and file system journaling. NTFS also supports shadow copy to allow backups of a system while it is running, but the functionality of the shadow copies varies between different versions of Windows.

<span class="mw-page-title-main">Microsoft Outlook</span> Email and calendaring software

Microsoft Outlook is a personal information manager software system from Microsoft, available as a part of the Microsoft 365 software suites. Though primarily being popular as an email client for businesses, Outlook also includes functions such as calendaring, task managing, contact managing, note-taking, journal logging, web browsing, and RSS news aggregation.

<span class="mw-page-title-main">Outlook Express</span> Microsoft e-mail client software

Outlook Express, formerly known as Microsoft Internet Mail and News, is a discontinued email and news client included with Internet Explorer versions 3.0 through 6.0. As such, it was bundled with several versions of Microsoft Windows, from Windows 98 to Windows Server 2003, and was available for Windows 3.x, Windows NT 3.51, Windows 95, Mac System 7, Mac OS 8, and Mac OS 9. In Windows Vista, Outlook Express was superseded by Windows Mail.

ZIP is an archive file format that supports lossless data compression. A ZIP file may contain one or more files or directories that may have been compressed. The ZIP file format permits a number of compression algorithms, though DEFLATE is the most common. This format was originally created in 1989 and was first implemented in PKWARE, Inc.'s PKZIP utility, as a replacement for the previous ARC compression format by Thom Henderson. The ZIP format was then quickly supported by many software utilities other than PKZIP. Microsoft has included built-in ZIP support in versions of Microsoft Windows since 1998 via the "Plus! 98" addon for Windows 98. Native support was added as of the year 2000 in Windows ME. Apple has included built-in ZIP support in Mac OS X 10.3 and later. Most free operating systems have built in support for ZIP in similar manners to Windows and macOS.

<span class="mw-page-title-main">Server Message Block</span> Network communication protocol for providing shared access to resources

Server Message Block (SMB) is a communication protocol used to share files, printers, serial ports, and miscellaneous communications between nodes on a network. On Microsoft Windows, the SMB implementation consists of two vaguely named Windows services: "Server" and "Workstation". It uses NTLM or Kerberos protocols for user authentication. It also provides an authenticated inter-process communication (IPC) mechanism.

<span class="mw-page-title-main">The Bat!</span> Email client for Windows

The Bat! is an email client for the Microsoft Windows operating system, developed by Moldovan software company Ritlabs. It is sold as shareware and offered in three editions: Home Edition, Professional Edition, and Voyager which is a portable version and is included with Professional Edition.

The Encrypting File System (EFS) on Microsoft Windows is a feature introduced in version 3.0 of NTFS that provides filesystem-level encryption. The technology enables files to be transparently encrypted to protect confidential data from attackers with physical access to the computer.

<span class="mw-page-title-main">Microsoft Entourage</span> Email client and personal information manager

Microsoft Entourage is a discontinued e-mail client and personal information manager that was developed by Microsoft for Mac OS 8.5 and later. 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 the classic Mac OS included Outlook Express 5. The last version was Entourage: Mac 2008, part of Microsoft Office 2008 for Mac, released on January 15, 2008. Entourage was replaced by Outlook for Macintosh in Microsoft Office for Mac 2011, released on October 26, 2010.

The following tables compare general and technical features of notable email client programs.

In a Windows network, NT LAN Manager (NTLM) is a suite of Microsoft security protocols intended to provide authentication, integrity, and confidentiality to users. NTLM is the successor to the authentication protocol in Microsoft LAN Manager (LANMAN), an older Microsoft product. The NTLM protocol suite is implemented in a Security Support Provider, which combines the LAN Manager authentication protocol, NTLMv1, NTLMv2 and NTLM2 Session protocols in a single package. Whether these protocols are used or can be used on a system which is governed by Group Policy settings, for which different versions of Windows have different default settings.

<span class="mw-page-title-main">Windows Address Book</span> Address book application used in Windows XP and before.

Windows Address Book was a component of Microsoft Windows that lets users keep a single list of contacts that can be shared by multiple programs. It is most commonly used by Outlook Express. It was introduced with Internet Explorer 3 in 1996 and improved in subsequent versions. The Windows Address Book API can query LDAP servers or read/write data to a local .wab file. In Windows Vista, Windows Address Book was replaced with Windows Contacts.

<span class="mw-page-title-main">Windows Live Mesh</span>

Windows Live Mesh is a discontinued free-to-use Internet-based file synchronization application by Microsoft designed to allow files and folders between two or more computers to be in sync with each other on Windows and Mac OS X computers or the Web via SkyDrive. Windows Live Mesh also enabled remote desktop access via the Internet.

Data Protection Application Programming Interface (DPAPI) is a simple cryptographic application programming interface available as a built-in component in Windows 2000 and later versions of Microsoft Windows operating systems. In theory, the Data Protection API can enable symmetric encryption of any kind of data; in practice, its primary use in the Windows operating system is to perform symmetric encryption of asymmetric private keys, using a user or system secret as a significant contribution of entropy. A detailed analysis of DPAPI inner-workings was published in 2011 by Bursztein et al.

The following tables compare general and technical information for a number of file systems.

<span class="mw-page-title-main">OneDrive</span> File hosting and synchronization service operated by Microsoft

Microsoft OneDrive is a file-hosting service operated by Microsoft. First released in August 2007, it allows registered users to store, share and sync their files. OneDrive also works as the storage backend of the web version of Microsoft 365 / Office. OneDrive offers 5 GB of storage space free of charge, with 100 GB, 1 TB, and 6 TB storage options available either separately or with Microsoft 365 subscriptions.

This is a comparison of online backup services.

An rpmsg file is a file format containing a restricted-permission message. It is used to implement IRM for Outlook messages with the aim of controlling access to content via encryption and access controls, and restricting certain actions such as the ability to forward or copy.

Exchange ActiveSync is a proprietary protocol designed for the synchronization of email, contacts, calendar, tasks, and notes from a messaging server to a smartphone or other mobile devices. The protocol also provides mobile device management and policy controls. The protocol is based on XML. The mobile device communicates over HTTP or HTTPS.

<span class="mw-page-title-main">Recovery Toolbox</span> Microsoft windows recovery software

Recovery Toolbox is a family of tools and online services for recovering corrupted files, file formats, and recovering passwords for various programs.

References

  1. ↑ OST to PST Converter: Free and Manual Methods to Convert OST to PST , retrieved 2021-12-03
  2. 1 2 "Introduction to Personal Folders files (.pst)". Microsoft.com. Retrieved 2008-10-04.
  3. ↑ "Reduce the size of a .pst file". Microsoft.com. Retrieved 2015-10-21.
  4. ↑ "Create a .pst file in Outlook 2003/Office Outlook 2007 format". Microsoft.com. Retrieved 2008-10-04.
  5. ↑ "XCLN: Improving the Security of PST Files". Microsoft.com. Retrieved 2009-08-12.
  6. ↑ [MS-PST]: Outlook Personal Folders File Format (.pst) Structure Specification
  7. ↑ Migrating from Microsoft Outlook to Gmail
  8. ↑ "Binary analysis of the pst file format" . Retrieved 2010-06-12.
  9. ↑ "[MS-PST]: Outlook Personal Folders (.pst) File Format - 2.2.2.6 HEADER". Microsoft. Retrieved 2014-10-07.
  10. 1 2 "The .pst file has a different format and folder size limit in Outlook 2007 and in Outlook 2003 (KB830336)". Microsoft. 2007-02-05. Retrieved 2007-03-05.
  11. ↑ "The file size limits of .pst and .ost files are larger in Outlook 2010 (KB982577)". Microsoft. 2011-09-02. Retrieved 2011-12-08.
  12. ↑ "How to configure the size limit for both (.pst) and (.ost) files in Outlook 2007 and in Outlook 2003 (KB832925)". Microsoft. 2007-02-13. Retrieved 2008-04-09.
  13. ↑ "Introducing Office for Mac 2011: The Quintessential Teammate". Microsoft.com. Retrieved 2010-07-09.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.