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
Dec 24, 2023 9:24am 15.0.2 0 VERSION_BUMP 9c677338
Mar 29, 2023 6:50pm 15.0.2 0 VERSION_BUMP 592677ca
Oct 25, 2022 12:07pm 15.0.0 0 VERSION_BUMP 8426d57a
Jun 30, 2022 8:45am 14.1.3 0 VERSION_BUMP 0266a531
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