---
title: winmail.dat Attachments
description: "**Tool:** WebMailPRO **Category:** Email / Attachments **Updated:** 2025 --- #### Overview Some WebMailPRO users may receive an attachment named **winmail.dat** instead of the file the sender intended to include. This file is generated by **Microsoft Outlook** and **Microsoft Exchange** when…"
url: "https://www.k12usa.com/docs/winmail-dat-attachments/"
updated: "2025-12-04"
category: K12SchoolBits
tags:
  - K12SchoolBits
  - Microsoft Outlook
  - WebMailPRO
---

# winmail.dat Attachments

**Tool:** WebMailPRO
 **Category:** Email / Attachments
 **Updated:** 2025

---

#### Overview

Some WebMailPRO users may receive an attachment named **winmail.dat** instead of the file the sender intended to include.

This file is generated by **Microsoft Outlook** and **Microsoft Exchange** when the sender’s email is sent using **Rich Text Format (RTF)** or when Outlook has been configured to use a Microsoft-only encoding method.

WebMailPRO cannot decode winmail.dat files. The issue must be corrected **by the sender.**

---

#### Why This Happens

Outlook and Exchange use a proprietary Microsoft format called **TNEF** (Transport Neutral Encapsulation Format) when sending RTF-formatted messages.

When sent to non-Microsoft mail systems (including WebMailPRO), the message appears as:

- A simplified or plain-text body
- A single attachment named **winmail.dat**
- The intended files (PDFs, Word documents, images, etc.) embedded inside the TNEF package

Because WebMailPRO does not support TNEF decoding, the original attachments are not accessible.

---

#### How WebMailPRO Handles winmail.dat

**WebMailPRO** does not unpack, interpret, or extract content from **TNEF**-encoded messages.
 Therefore:

- The winmail.dat file cannot be opened
- The original attachments are not visible
- The message may appear incomplete

The only solution is for the **sender** to adjust their Outlook or Exchange settings.

---

#### Fixing the Problem (Sender Must Make the Change)

Provide the following guidance to the sender:

##### Option 1 — Use HTML or Plain Text in Outlook

1. Outlook → **File → Options → Mail**
2. Under *Compose messages in this format*, select:
   - **HTML** *(recommended)*
   - or **Plain Text**

This prevents Outlook from using TNEF.

---

##### Option 2 — Fix the Individual Contact Entry

Outlook may store per-contact formatting preferences.
 To correct:

- Open the contact in Outlook
- Double-click the email address
- Change *Internet format* to **Let Outlook decide the best sending format**

This often resolves repeated **winmail.dat** problems for specific recipients.

---

##### Option 3 — Fix Office 365 / Exchange Online Settings

The sender’s administrator can globally disable TNEF for external recipients:

- Microsoft 365 Admin Center → **Exchange Admin Center**
- **Mail Flow** → **Remote Domains** → **Default**
- Set **Use Rich Text Format = Never**

This ensures all external mail uses HTML or Plain Text automatically.

---

#### Temporary Workarounds for WebMailPRO Users

If the sender cannot change settings immediately, the WebMailPRO user may:

- Ask the sender to resend the file using **HTML** or **Plain Text** format
- Ask the sender to upload the file to a shared drive and send a link instead

**Security Note:**
 Various online winmail.dat “extractors” exist, but they may expose private or sensitive information.
 **We do not recommend using them.**

---

#### Summary

- **winmail.dat** attachments are created by **Outlook/Exchange**, not WebMailPRO
- The problem must be fixed on the **sender’s side**
- Once the sender switches to HTML or Plain Text, attachments will appear normally

---

#### References / Further Reading (Microsoft & Authoritative Sources)

- **How TNEF affects email messages — Microsoft**
   [https://learn.microsoft.com/en-us/troubleshoot/outlook/message-body/how-tnef-affects-email-messages?utm_source=chatgpt.com](https://learn.microsoft.com/en-us/troubleshoot/outlook/message-body/how-tnef-affects-email-messages?utm_source=chatgpt.com)
- **Specify message format for external recipients — Exchange Online**
   [https://learn.microsoft.com/en-us/troubleshoot/exchange/send-emails/how-to-specify-email-message-format?utm_source=chatgpt.com](https://learn.microsoft.com/en-us/troubleshoot/exchange/send-emails/how-to-specify-email-message-format?utm_source=chatgpt.com)
- **Why am I getting winmail.dat? — Microsoft Q&A**
   [https://learn.microsoft.com/en-us/answers/questions/4652873/why-i-am-getting-email-attachments-as-winmail-dat?utm_source=chatgpt.com](https://learn.microsoft.com/en-us/answers/questions/4652873/why-i-am-getting-email-attachments-as-winmail-dat?utm_source=chatgpt.com)