Kopano Alternatives

Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.

A fully fledged, free email server solution, an open source project (GPL v2).

Kolab Groupware is a secure, scalable, reliable, flexible, full-featured collaboration suite.

Web-based IMAP email client

SOGo is groupware server with a focus on scalability and open standards.

Google's encompassing suite of cloud-based business apps.

An open source mailserver suite.

Microsoft Exchange Server is a messaging and collaborative software product developed by Microsoft.

Dovecot is an open source IMAP and POP3 email server for Linux/UNIX-like systems, written with...

Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.

hMailServer is a free e-mail server for Microsoft Windows.

Microsoft Teams provides the enterprise-level security, compliance and management features you expect from Office 365, including broad support for compliance standards, and eDiscovery and legal hold for channels, chats, and files.

Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!