fmail

Install command: 
brew install --cask fmail

Name: FMail

Unofficial native application for Fastmail

https://arievanboxel.fr/fmail/en/

Cask JSON API: /api/cask/fmail.json

Cask code: fmail.rb on GitHub

Current version: 2.7.6

Requirements: macOS >= 11

Analytics:

Installs (30 days)
fmail 4
Installs (90 days)
fmail 17
Installs (365 days)
fmail 69