Which MIME types are related to file extension ".nk2"?
The .nk2 file extension is associated with 1 MIME types:
A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.
About .nk2 Files
NK2 files are binary files used by Microsoft Outlook to store an auto-complete list of email addresses.
They are commonly called Nickfiles and use the MIME type application/octet-stream, which indicates that the file contains raw binary data.
- Main use: Storing frequently used email addresses for quick recipient lookup when composing emails.
- Data transfer: They can assist in transferring Outlook nickname data between systems.
- Software compatibility: Microsoft Outlook (notably versions 2007 through 2010) is designed to generate and manage these files.
Relationship between file extension and MIME type
A file extension is a suffix at the end of a filename that indicates what type of file it is. File extensions help both users and operating systems identify what application should be used to open the file.
File extensions are typically separated from the filename by a period (dot) and consist of 2-4 characters, though they can be longer. For example, in the filename "document.pdf", ".pdf" is the file extension.
File extensions are closely related to MIME types, as they both serve to identify the format of a file. However, while MIME types are used primarily by web browsers and servers, file extensions are used by operating systems and applications.
Associated MIME types
FAQs
What is an NK2 file?
An NK2 file is a nickname cache file used by older versions of Microsoft Outlook (primarily 2002 through 2010). It stores the Auto-Complete list, which consists of email addresses and names you have previously typed, allowing Outlook to suggest recipients as you compose new emails.
How do I open or view an NK2 file?
You cannot open an NK2 file with standard text editors like Notepad because it is a binary file. To view or edit the contacts inside, you must use specialized third-party software such as NirSoft NK2Edit.
Where are NK2 files located on my computer?
On Windows systems running older versions of Outlook, these files are typically found in the hidden folder %APPDATA%\Microsoft\Outlook. You can paste this path into the Windows File Explorer address bar to access the directory.
How do I import an NK2 file into Outlook 2013, 2016, or newer?
Newer versions of Outlook use a .dat file in the RoamCache folder instead of .nk2. To import legacy data, place the .nk2 file in the Outlook AppData folder with the same name as your profile, then start Outlook using the command outlook.exe /importnk2 via the Windows Run dialog.
Can I edit an NK2 file with a text editor?
No, attempting to edit an .nk2 file with a text editor will likely corrupt it. The file uses the MIME type application/octet-stream, meaning it contains raw binary data that requires a dedicated editor to interpret correctly.
Why did my Outlook Auto-Complete list stop working?
If Outlook stops suggesting names, your .nk2 file may be corrupted. You can often fix this by renaming the existing file (e.g., to Outlook.nk2.old) and restarting Outlook to force it to create a fresh, empty Auto-Complete list.
What is the MIME type for NK2 files?
NK2 files are classified as application/octet-stream. This is a generic designation for binary files that do not have a specific text format. You can learn more about this category on the application/octet-stream page at mime-type.com.
General FAQ
What is a MIME type?
A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.
MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.
MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.
How do I find the MIME type for a file?
You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.
Why can one extension have multiple MIME types?
Different programs and historical usage may assign various MIME identifiers to the same file format. Listing them together helps maintain compatibility across tools.