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What are TNEF files and how to open them

Are you having problems opening a TNEF file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your TNEF files.

What is a TNEF file?

A .TNEF file is a Transport Neutral Encapsulation Format file.

TNEF stands for Transport Neutral Encapsulation Format. It’s an email attachment format that Microsoft created to allow sending files in a universal binary format. TNEF is also known as Outlook Rich Text Format. Microsoft Outlook uses TNEF to send attachments. Microsoft Exchange Server also uses it.

Email attachments sent using this format are usually named "winmail.dat" and are therefore saved with the .dat file extension instead of .tnef. You can find various winmail.dat openers on our page about file extension DAT.

How to open TNEF files

Important: Different programs may use files with the TNEF file extension for different purposes, so unless you are sure which format your TNEF file is, you may need to try a few different programs.

We have not yet verified any programs for Windows that work with this specific file format. If you know one, please use the 'Suggest a program' link below. Thanks!

Last updated: May 27, 2024

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