Microsoft Outlook uses the Nickfile (NK2) to store e-mail address aliases.
The file is also known as Outlook AutoComplete File and Nickname file.
The actual mime type of the NK2 format is unspecified
The NK2 has the following file signature:
hexadecimal: 0D F0 AD BA
Note that other sources claim that the file signature is
hexadecimal: 0D F0 AD BA 0A 00 00 00
The NK2 basically contains a list of items. The attributes of these items are defined by the Microsoft Outlook Message API (MAPI).