thunderbird@esr

Install command: 
brew install --cask thunderbird@esr

Names: Mozilla Thunderbird ESR, Mozilla Thunderbird Extended Support Release

Customizable email client

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

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

Cask code: thunderbird@esr.rb on GitHub

Current version: 140.5.0esr

Requirements: macOS >= 10.15

Conflicts with casks:

thunderbird 144.0.1 Customizable email client Mozilla Thunderbird

Analytics:

Installs (30 days)
thunderbird@esr 38
Installs (90 days)
thunderbird@esr 96
Installs (365 days)
thunderbird@esr 808