Kolab Now Alternatives for Mac OS X

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.

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.

Kopano is a versatile open-source groupware suite offering email, calendaring, contacts, and online collaboration tools for businesses and organizations. It provides flexible deployment options, including on-premises and hosted solutions, with strong focus on data privacy and security.

Mailvelope is a free and open-source browser extension for Chrome and Firefox that brings end-to-end encryption to your existing webmail services using the OpenPGP standard. It allows users to encrypt, decrypt, and digitally sign emails directly within their web browser, enhancing privacy and security without requiring a change in email provider.

GPGMail is a robust extension for Apple Mail, seamlessly integrating OpenPGP encryption and digital signatures directly into your email workflow for enhanced privacy and security.