letter-opener

Install command: 
brew install --cask letter-opener

Name: Letter Opener

Display winmail.dat files directly in Mail.app

https://winmail.help/

Cask JSON API: /api/cask/letter-opener.json

Cask code: letter-opener.rb on GitHub

Current version: 16.0.7

Requirements: macOS >= 10.14

Analytics:

Installs (30 days)
letter-opener 0
Installs (90 days)
letter-opener 6
Installs (365 days)
letter-opener 60