---
type: concept
title: winmail.dat (TNEF)
tags: [microsoft-outlook, interoperability, email]
related: [microsoft-outlook, mozilla-thunderbird]
created: 2026-07-01
updated: 2026-07-01
sources: ["output/rz_uni_greifswald_de_support_faq_e_mail.md"]
---

# winmail.dat (TNEF)

`winmail.dat` is a proprietary attachment format created by **Microsoft Outlook** and **Exchange** when using the **Rich-Text Format (RTF)** for emails sent to "Internet recipients" (users of non-Microsoft email providers).

## Technical Nature
The `winmail.dat` file contains:
- Formatting information for the email text.
- The actual file attachments that were intended for the recipient.

Because it is a proprietary Microsoft format, most other email clients cannot interpret it natively and instead display it as a `winmail.dat` attachment.

## Recovery Tools
To read the contents of a `winmail.dat` file in other clients, the following extensions/tools are recommended:
- **Mozilla Thunderbird**: [[queries/lookout-fix]] (LookOut fix extension).
- **Mac Mail**: **TNEF's Enough**.