Best Open Source Microsoft Exchange Alternatives in 2022

Open source alternatives to Microsoft Exchange can give you more flexibility and customization options for your email hosting without breaking the bank. However, they also require a considerable amount of technical expertise and effort to maintain compared to proprietary email hosting servers like Microsoft Exchange. To be sure the benefits of open source solutions outweigh the costs, consider the top options and compare them with your email hosting needs. 

Open source alternatives to Microsoft Exchange

If you currently use Microsoft Exchange or are considering it, the following open source tools might be a suitable alternative:


Zimbra is a fully-featured open source email server with many proprietary add-ons. It includes all the expected productivity tools: 

  • Email
  • File sharing
  • Contact management
  • Calendar and schedule management
  • Instant messaging

Zimbra offers many competitive features, including buddy lists, status management, emoji support, and integration with external calendar and mail accounts. You can use the Zimbra web or desktop application as well as mobile apps for iOS and Android devices. This software is available as a free edition, a paid managed service, or an licensed on-premises deployment.


Unlike some of the other vendors on this list, SOGo is a completely free tool to use under the General Public License (GPL). This means you can create a customized, branded email environment without paying a single license fee. 

Plus, SOGo was developed with scalability in mind; a single SOGo server can support thousands of users, so it’s easy to add new users to your email server as your business grows. SOGo supports most major email clients, but it was specifically designed for interoperability with Mozilla Thunderbird.


Open-Xchange (also called the OX App Suite) has the cleanest user interface of all the email hosting solutions on this list. Its features and pricing structure are more appropriate for midsize to large businesses, but the web-based UI and navigation are competitive with Microsoft Exchange or Office 365. 

The OX App Suite includes all the email essentials as well as premium add-ons including collaboration apps, file transferring, and anti-malware security features. Many web hosting and internet service providers use Open-Xchange as the basis for their email hosting services, so it can be an impactful tool if you have the means to configure and maintain it.

Kopano ONE

Kopano ONE is a self-hosted email and calendaring server that was built specifically for SMBs. It is intended for environments with 250 users or fewer and can be accessed from any operating system or browser.

The broader Kopano Groupware is based on the now-defunct Zarafa open source software, which was included in the Fedora Linux operating system and offered native Outlook support. As such, you can use Kopano ONE alongside Office 365 applications without needing to use the Exchange server.


Citadel is an all-in-one messaging and collaboration server that runs on Linux, BSD, Solaris, and other Unix-based operating systems. It includes email, group scheduling and calendaring, shared contacts, mail list server, instant messaging, public folders, and mobile device support. Citadel supports distributed installation across multiple servers for scaling and high availability, plus Web access and local clients.

It’s easy to administer, and many deployments can take as little as one hour. One of the biggest benefits of using Citadel, however, is that it’s completely unrestricted. This means you can modify the Citadel source code to add a specific feature or customization you want, as long as you know how to code and configure it.

Open source cost vs. time requirements

The tools in this list are more affordable and can be more impactful than Microsoft Exchange, but they require a considerable amount of time and effort to maintain. If you want to control your email data or customize your hosting capabilities and can afford to maintain an email server on your own, one of these solutions might meet your needs.

On the other hand, popular email services like Exchange and Gmail are usually much easier to manage. They come with a higher price tag, but you won’t be burdened with the ins and outs of email server maintenance. Ultimately, you’ll need to determine whether you can afford to spend more time or more money on an email hosting solution.

Read next: How to Choose Email Hosting for A Growing Business

This article was originally published on May 4, 2011. It was updated by Kaiti Norton.

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