iMail

Fast, safe, heavy mail solution.

Citadel

Is a collaboration suite (messaging and groupware).

Turnkey Solutions for the Enterprise Cloud

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

KerioConnect is a commercial mail and groupware server.

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

Sharing & communication software for business

Low cost, easy to use Email Server software for virtual, on-premise, or hosted deployments for…

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

Open-Xchange Server 6 is the most advanced Linux based Groupware solution f.

OpenChange aims to provide a portable Open Source implementation of Microsoft Exchange Server and…

PowerMTA is an industrial-strength software for high-volume email delivery.

Alternative, self-hosted private mail system. End-to-end encryption for messages and attachments.

Web-based IMAP email client

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

Sanwhole Exchange is a server running iMail, iPress and iStore services.

Linux directory, domain, mail, gateway and infrastructure server for SMBs.

Zimbra Collaboration is an open, secure collaboration tool for email, calendaring, tasks and more.

Zoho is an all-in-one online office suite.

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