Evolution is the official personal information manager for GNOME.

Gpg4win is an email and file encryption package for most versions of Microsoft Windows, which uses GnuPG public-key cryptography for data encryption.

GPGTools which lets you send and receive secure, OpenPGP encrypted and signed messages.

The Bat! is an email program for Windows that protects the correspondence and empowers the users to handle large amounts of emails quickly and efficiently.

Seahorse is a GNOME application for managing encryption keys and passwords in the GnomeKeyring.

MailMate is an IMAP email client for macOS featuring extensive keyboard control, Markdown integrated email composition, advanced search conditions.