Files in an Operating System or an application are encrypted in order to save them from corruption and possible data theft. When you create a new file on your computer, you can choose one of three levels of encryption settings. Once the file has been created, you can not change these security settings.
The chosen encryption technique will be used to encode the PST file under consideration. Once the file has been encrypted, no other program can read this file. In order to secure data in a PST file, you can use Windows BitLocker Drive encryption system or Encryption File System. Only a basic level of security is ensured by using compressible encryption and superior encryption.
If you choose 'no encryption' option during creation, PST file will not be encoded. You can even use a text editor to read the PST file if it has not undergone any encryption. Any hexadecimal editor can be used to view the contents of such files. A compressible encryption can be used to encode PST files in formats suitable for compression. You will need to have a compression program installed. A file encoded with this option can not be read by the text editor or hexadecimal editor.
For higher protection, you can choose the third encryption option – 'higher encryption'. If you have disk compression programs installed on your computer, you can still use them to compress files. However, level of compression will be lower than that of 'compressible encryption' option mentioned above. Files encoded with 'higher encryption' method can not be read by any text editor. If you have not paid attention to encryption techniques so far, you have been encoding your PST files with default option of 'compressible encryption'.
Source by Jim Johannasen