Apps to Mail Filtering

Disroot is a Free and Open-Source Software (FOSS) project offering privacy-focused online services, primarily secure email, alongside collaborative tools like cloud storage, document editors, and file sharing, all under a strong commitment to user anonymity and decentralization.

Horde Groupware is a free, web-based suite of applications designed for collaboration and productivity. Built on the robust Horde framework, it offers a comprehensive set of tools including webmail, calendar, task management, and note-taking, providing an integrated platform for individuals and teams.

Enigmail is a robust extension for Mozilla Thunderbird and SeaMonkey, providing comprehensive OpenPGP encryption and digital signing for your email communications. It integrates seamlessly into these email clients, offering a user-friendly way to protect your privacy and ensure the authenticity of your messages.

Mailpile is a free and open-source webmail client designed with privacy and encryption as core principles. It offers a self-hostable solution for managing your email with built-in support for PGP encryption and other security features, providing an alternative to traditional webmail services.

K-9 Mail is a free and open-source email client for Android, renowned for its focus on privacy, security, and extensive customization options. It supports multiple account types including IMAP, POP3, and Exchange.

ProtonMail is a leading secure email service utilizing end-to-end encryption and zero-access architecture to protect user privacy. Developed by scientists at CERN, it offers a robust and user-friendly platform for sending and receiving confidential communications.