SOGo
SOGo is groupware server with a focus on scalability and open standards.
19 Alternatives To SOGo
Afterlogic Webmail
Webmail is an open-source webmail script for existing IMAP servers.
G Suite
Google’s encompassing suite of cloud-based business apps.
Horde
Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Kolab Community
Kolab Groupware is a secure, scalable, reliable, flexible, full-featured collaboration suite.
Kopano
Sharing & communication software for business
Mailpile
Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features.
Mailspring
Mailspring is a mail client for Mac, Windows and Linux.
Microsoft Exchange Server
Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.
Mu4e
Starting with version 0.9.8, mu provides an emacs-based e-mail client which uses mu as its back-end: mu4e.
NeutronMail
Self-hosted server for the ProtonMail client.
ProtonMail
Secure email with absolutely no compromises. Get your free encrypted email account today.
Radicale
The Radicale Project is a complete CalDAV (calendar) and CardDAV (contact) server solution.
Rainloop
RainLoop is a web based email client.
Roundcube
Web-based IMAP email client
Squirrelmail
SquirrelMail is a standards-based webmail package written in PHP.
Tutanota
Get your encrypted mailbox for free.
Zentyal
Linux directory, domain, mail, gateway and infrastructure server for SMBs.
Zimbra Collaboration Suite
Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more.
iRedMail
A fully fledged, free email server solution, an open source project (GPL v2).