Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
docNCRYPT - docNCRYPT is a cybersecurity platform which only focuses on its core services in protecting your email directly from the different email service provider and allows you to integrate your business email portal in the online service.
Roundcube - Web-based IMAP email client
LuxSci - LuxSci providing HIPAA-compliant email, secure email & web services.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.
encryptomatic - encryptomatic is a smart email encryption software which provides tons of tools in encryption protocols for secure communication and business transaction.