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What are TNEF files and how to open them

Are you having problems opening a TNEF file or just wondering what they contain? We explain what these files are used for and show you software that we know can open or otherwise handle your 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

We have identified one TNEF opener that is compatible with this specific type of TNEF file.

Programs that open Transport Neutral Encapsulation Format files

Last updated: February 24, 2023

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