MessageOne - MessageOne offers email management solutions such as EMS and AlertFind for archiving, e-discovery, security and notification services.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Vade Secure - Email security to protect against email-borne phishing, spear phishing, malware, and ransomware. Email security and management based on artificial intelligence.
Roundcube - Web-based IMAP email client
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.