Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
Gpg4win (GNU Privacy Guard for Windows) is encryption software for files and emails.
MsgSafe.io provides private, encrypted, online communication with layers of security you can trust.
The Bat! is a secure email client software, built to protect your correspondence against third-parties. .
MailMate is an IMAP email client for Mac featuring extensive keyboard control, Markdown supported email composition.
Kopano puts an email, video meetings, calendaring, and file sharing solution within one single interface.
Need a great working email client on Android? MailDroid is the one you should download! Has the power of Outlook and Thunderbird for your Android device.
CipherMail for Android is an Android application which can be used with your existing Android mail application to send and receive S/MIME digitally signed and encrypted email with an Android smartphone.