GPGMail is described as 'PGP plugin for Apple Mail. It brings the functionality to sign, verify, encrypt and decrypt mails using the OpenPGP standard' and is an app in the Security & Privacy category. There are more than 10 alternatives to GPGMail for a variety of platforms, including Online / Web-based, Linux, Mac, Windows and Android. The best alternative is ProtonMail, which is both free and Open Source. Other great apps like GPGMail are Tutanota (Freemium, Open Source), mailbox.org (Paid), Enigmail (Free, Open Source) and Mailvelope (Free, Open Source).
mailbox.org offers a secure e-mail account for home and business use. The domain name, email@example.com, is easy to remember and can be understood anywhere in the world. They have been operating e-mail accounts for more than 20 years and are a highly reliable service provider.
Mailvelope is a browser extension that allows to exchange encrypted emails following the OpenPGP encryption standard. Mailvelope integrates directly into the Webmail user interface, it's elements are unintrusive and easy to use in your normal workflow.
ElectronMail is an Electron-based unofficial desktop client for ProtonMail and Tutanota end-to-end encrypted email providers. The app aims to provide enhanced desktop user experience enabling features that are not supported by the official in-browser web clients.