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TNEF Attachment Extractor

TNEF Attachment Extractor

What is the TNEF file format?

Transport Neutral Encapsulation Format or TNEF is a proprietary email attachment format used by Microsoft Outlook and Microsoft Exchange Server. An attached file with TNEF encoding is most often named winmail.dat or win.dat, and has a MIME type of Application/MS-TNEF. The official (IANA) media type, however, is application/

Sample request schema:

This API endpoint expects in the request body a JSON with a “content” property


content: “BASE-64 encoded string of a TNEF file”


For quick testing you can convert your winmail.dat (TNEF encoded file) into a base-64 encoded string with online converter:

Otherwise you need to implement this conversion logic in your client prior to calling this API endpoint.

As a result this endpoint will return base-64 encoded files and its original file names.

Sample result schema:





To quickly check and convert the result base-64 strings back you could also use this online converter tool:

Use case

Some email clients or third party applications that receive emails cannot interpret the TNEF-encoded file that comes from users that are using Microsoft Outlook as their main email client to send their emails with having the TNEF feature activated. With a custom implementation /business process flow that is using our API it would be still possible to parse out and extract the attachted documents in order to store these files on your client or in your third party application.

More information on how Microsoft Outlook can be configured in this regard here:



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