thunderbird@beta

Install command: 
brew install --cask thunderbird@beta

Name: Mozilla Thunderbird Beta

Customizable email client

https://www.thunderbird.net/en-US/download/beta/

Cask JSON API: /api/cask/thunderbird@beta.json

Cask code: thunderbird@beta.rb on GitHub

Current version: 143.0b4

Requirements: macOS >= 10.15

Analytics:

Installs (30 days)
thunderbird@beta 17
Installs (90 days)
thunderbird@beta 50
Installs (365 days)
thunderbird@beta 206