Enigmail is described as 'security extension to Mozilla Thunderbird and SeaMonkey. It enables you to write and receive email messages signed and/or encrypted with the ' and is a popular app in the Security & Privacy category. There are more than 25 alternatives to Enigmail for a variety of platforms, including Mac, Linux, Windows, Online / Web-based and Android. The best alternative is Tutanota, which is both free and Open Source. Other great apps like Enigmail are GnuPG (Free, Open Source), mailbox.org (Paid), Mailvelope (Free, Open Source) and Vivaldi Mail (Free).
GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications.
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.