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-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. None the .pst data is stored as plain text. Compressible the .pst data is encrypted with a byte-substitution cipher 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 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 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. Formats and size The file is structured as a B-tree with 512 byte nodes and leaves. All PST files begin with the four-byte magic string "!BDN", a four-byte CRC number, and a two-byte magic string of "SM". 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 Although superseded, this format is supported all Outlook versions, by Internet Message Access Protocol Version 4rev1 (IMAP4) accounts and by HTTP accounts. From Outlook 2003 and onward, the