letter-opener ☆

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Description:
Display winmail.dat files directly in Mail.app

Type: Cask | Latest Version: 16.0.7@0 | Tracked Since: Dec 28, 2025

Links: Homepage | formulae.brew.sh

Category: Productivity

Tags: email utility mail-plugin productivity outlook

Install: brew install --cask letter-opener

About:
Letter Opener is a utility that integrates with macOS Mail.app to automatically decode and display the contents of TNEF-encoded winmail.dat attachments. It eliminates the need for third-party websites or separate applications by rendering the files directly within your native email client. This provides a seamless and secure workflow for users who frequently receive attachments from Microsoft Outlook users.

Key Features:

Seamless integration with macOS Mail.app
Automatic decoding of TNEF (winmail.dat) files
Renders embedded content inline, including appointments and contacts
No need for external tools or web services

Use Cases:

Corporate users receiving meeting invites and rich-text emails from Outlook users
Anyone needing to view the contents of winmail.dat attachments without hassle

Alternatives:

TNEF's Enough – A standalone application that requires manually opening winmail.dat files.
Online Decoders – Web services that require uploading sensitive attachments to a third-party server.

Version History

Detected	Version	Rev	Change	Commit
Sep 15, 2025 12:25pm	16.0.7	0	VERSION_BUMP	464f08b6
Aug 1, 2025 8:46pm	16.0.7	0	VERSION_BUMP	ce9c6313