Microsoft KB Archive/105138

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WFWG Mail: DoubleSpace and Highest Security Options

Article ID: 105138

Article Last Modified on 10/28/1999


  • Microsoft Windows for Workgroups 3.11

This article was previously published under Q105138


In version 3.11 of Microsoft Windows for Workgroups, there are additional menu items not supplied in the retail package of Microsoft Mail for PC Networks.

Under the Mail Options menu, there is a section titled "Optimize Local Mail File." The following new choices are available:

Highest Security

These two choices are specific to version 3.11 of Microsoft Windows for Workgroups Mail and are only available when running with MS-DOS version 6.0 or later.


DoubleSpace is considered to have less encryption (resulting in less security) but better performance (that is, increased speed) than the Highest Security option. DoubleSpace is available with MS-DOS version 6.0 or later only.

The Highest Security option uses the same Mail message file (.MMF) encryption algorithm that Microsoft Mail for PC Network uses. Highest Security is not as fast as DoubleSpace because time is used to encrypt and decrypt the .MMF file.

The DoubleSpace encryption is built into DoubleSpace itself. A file cannot be copied from a DoubleSpace drive, imported to a different computer, and easily read. Since the file allocation table (FAT) system is cluster-based, DoubleSpace uses its own FAT (which is called the Microsoft DoubleSpace FAT [MDFAT]) to achieve sector allocation. This encryption option is fast, however, it is not as secure as the encryption algorithm used in the Highest Security setting.

Additional information about DoubleSpace can be found on pages 118-136 in the MS-DOS "User's Guide" and in Chapter 3 of the MS-DOS "Technical Reference Manual."

Additional query words: double space WGPO

Keywords: KB105138