Is Zimbra Open Source? Yes! FAQs about Zimbra OSE for YOU! (updated August 2023)

Hello Zimbra Friends, Customer and Partners,

With the release of Zimbra 9, there have been many questions about Zimbra’s Open Source status and Synacor’s commitment to Open Source as a practice and a community. We listened to your questions and concerns, and here is a comprehensive list of FAQs for you.

If you have additional questions, please comment on the blog.

Many thanks,

Your Zimbra Team


Q: Is Zimbra still an Open Source product?

A: Yes. Zimbra 8.8.15 will remain Open Source, including compatibility in terms of CPAL, GNU Public license, etc. The Zimbra code repositories are still available on GitHub, providing access to the Open Source code. Zimbra 9 is Open Source, but the Zimbra Modern UI and some components in the Network Edition (which traditionally have not been included in the Open Source Edition) do not use Open Source licenses. 

Q: How to obtain a Zimbra Open Source build?

A: Install a fresh copy of a supported Operating System such as Ubuntu 20.04 then follow the steps under To build a specific patch at

Zimbra 9

Q: What is different about Zimbra 9?

A: The source code for Zimbra 9 is available in the Zimbra source code repository on GitHub. All client and server code is available for Zimbra 9 except the Modern UI code and components in the Network Edition that are closed source. Zimbra 9 binaries are only available via a Network Edition license. In summary, there are two changes in Zimbra 9 regarding Open Source. First, the Modern UI uses a commercial license (similar to Network Edition components).  Second, Zimbra 9 open source binaries are not being provided.


Q: Will anyone have access to the Modern UI code?

A: Customers with a valid Zimbra 9 license are allowed access to the Modern UI code. Their sales representative can coordinate access to the source code. These customers can also submit changes and contributions for this code.


Q: How can I get a free version of Zimbra 9?

A: Except for the Modern UI and Network Edition components, you can build Zimbra 9 binaries just like you can for Zimbra 8. When using these binaries, please remember to adhere to the license and terms of use as defined in


Q: What are the licensing terms for Zimbra 9?

A: Please refer to


Q: Will the open source code benefit from any supporting software upgrades that are delivered as part of Zimbra 9?

A: Except for the Zimbra 9 Modern UI code and components in the Network Edition, other updates will be part of the Open Source Edition. For example, if we modify the version of SpamAssassin or Postfix in Zimbra, those updates would become available in the Open Source Edition.


Q: What happens to Zimbra Open Source Edition when Zimbra 8.8.15 reaches end-of-life or end of technical guidance?

A: Zimbra will remain Open Source, except for the Modern UI and Network Edition components.


Q: Where is Zimbra Open Source code available?

A: The source code is available in the official Zimbra source code repository on GitHub (


Q: What is available in the Zimbra GitHub repository for Zimbra 9 and what is missing?

A: The Zimbra GitHub repository contains the Zimbra 9 product minus the Modern UI, any Zimlets built for the Modern UI and any Network Edition components.



Q: What is the difference between commercial offerings and having published source code?

A: Commercial offerings are provided by companies who sell licenses for the use of their software. Open Source systems are released under a license in which the copyright holder grants users the rights to change and distribute the software. These open source systems are typically overseen by a community of developers who contribute modifications to improve the product. 

Historically, Synacor has provided an Open Source Edition for these reasons:

  1. Try Before You Buy – Customers can run the Zimbra Open Source Edition to verify that Zimbra meets their needs. In some cases, they determine that they need more features and/or support, and they upgrade to Zimbra Network Edition.
  2. Security – Some organizations have a mandate to only use Open Source solutions for security reasons, e.g., governments.
  3. Quality – Open source allows 3rd party developers to isolate and fix bugs that are critical to their environments.

These options are still available with Zimbra. Try Before You Buy customers can use free Zimbra trial licenses. Security and Quality customers can: 

  • Use the open source versions of Zimbra 8.8.15 or Zimbra 9. 
  • Purchase a Zimbra 9 license if they need access to the commercially-licensed source code. 

Finally, some Small/Medium Business (SMB) owners use the Zimbra Open Source Edition because they cannot afford minimum license fees. 


Q: Will we still be able to say we are Open Source as a sales differentiator?

A: Yes. Zimbra 8.8.15 is fully Open Source and remains the market leader for installations and usage. Zimbra 9 has an Open Source core and applies in customer situations where software licensing and access to maintenance are requirements.


Q: Does Zimbra still meet all the licensing requirements for Open Source software if a portion of the code is no longer Open Source?

A: Yes. There is no real change with Zimbra 9. Zimbra 8.8.15 also has components that are not Open Source, e.g., Network Edition.


Q: What does Open Core mean?

A: Open Core means that the large majority of the Zimbra product is Open Source, i.e., everything except for the Modern UI and components in the Network Edition that traditionally have not been included in the Open Source Edition.


Q: Are Zimlets Open Source?

A: Synacor is committed to ensuring 3rd party developers are able to extend Zimbra through the development of Zimlets. To aid in that development, Synacor may make Zimlets Open Source, depending on the requirements and code samples made available to 3rd party developers. 

With a product that has a proprietary license and the ability to provide extensions, there is nothing from a licensing perspective that prevents a 3rd party from creating an extension/add-in and providing a license for it. Compare this licensing to creating a browser extension for Safari or an “Add-in” for MS Outlook. Both can be licensed with any appropriate license (based on dependencies), despite the fact that the underlying application is released with a closed-source, proprietary license. If Synacor or a 3rd party decides to open source their Zimlet code, they should pay attention to and use the appropriate open source licenses. For example, if a 3rd party developer used the zm-api-js-client library (a javascript and GraphQL client for making requests against the Zimbra SOAP API), they would have to abide by the BSD-3-clause license. In other words, the appropriate license is not based on the license of the product; the appropriate license is based on the license of the specific code being used/leveraged by the Zimlet.  


Government & Other Open Source Mandate Customers

Q: Will there still be a Zimbra Open Source Edition available for customers with a mandate for Open Source software?

A: Yes. Zimbra 8.8.15 can be used by customers who have Open Source mandates. Synacor will support Zimbra 8.8.15 until at least 12/31/23 with patches and security fixes (general support). Zimbra 9 is also an open source option, excluding the Modern UI and Network Edition components.


Q: Open Source is vital to meet Government contract requirements (security, privacy, data sovereignty). Does Zimbra still do that?

A: Yes. Zimbra 8.8.15 remains an option for governments who require Open Source, data sovereignty, privacy, security and customizations to meet local requirements. Zimbra 9 is also an open source option, excluding the Modern UI and Network Edition components (similar to Zimbra 8.8.15 Network Edition components, ZCO, etc.). Zimbra 9 is an option where security, privacy and data sovereignty are fundamental requirements.


Q: Can Zimbra still provide data sovereignty if a portion of the source code is not Open Source?

A: Yes. There is no change in the code from something which was previously open source to something that is not. The Modern UI is simply an additional component that has been added in much the same way as adding a new NE component. Under data sovereignty, data is subject to the laws within the nation under which it is collected. Many countries have passed various laws around control and storage of data. Zimbra is committed to adhering to those security and privacy laws, e.g., GDPR, CCPA and others.


Open Source Community

Q: What is Synacor’s commitment to Open Source and the philosophy of being open?

A: Synacor remains committed to our customers who have a mandate for Open Source software, and we will continue to enable our customers to Try Before They Buy. Synacor will also continue to accept Zimbra Open Source contributions and invest in Open Source projects like Zimbra and Preact (the technology used to build the Zimbra Modern UI).


Q: Can I still submit changes to the source code?

A: Yes. There is no change to the code contribution process. Anyone with access to the source code can submit changes and contributions. Please see the Zimbra Contribution Agreement (, which has not changed.


Q: Is there going to be a way for the open source community to report bugs?

A: Customers can submit bugs through the Zimbra Support Portal ( Non-customers can submit bugs via the Developers channel in the Zimbra forums ( Synacor will now be more actively involved in monitoring the Zimbra forums. In the near future, Synacor will publish information on how we intend to provide more transparency on which bugs are being prioritized/fixed.


Q: What is the process for customers when a Zimbra Network Edition license expires for Zimbra 9?

A: When the Network Edition license expires on Zimbra 8.8.15, the server defaults to the feature set of the Open Source Edition. Zimbra 9 does not include a FOSS binary release; therefore, there is no mechanism to fallback to FOSS. If the license ending date has passed, the 30 day grace period has expired, and the customer decides not to obtain a new license, the customer can resolve these issues by building the Zimbra 9 binaries and installing them on top of their existing Zimbra Network Edition system.



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7 Responses to Is Zimbra Open Source? Yes! FAQs about Zimbra OSE for YOU! (updated August 2023)

  1. Jochen Schüler May 13, 2020 at 11:25 PM #

    When will a Zimbra 9 Version appear on the website for download? Until this point I do not believe in the Open Source commitment.

    • Gayle Billat June 5, 2020 at 4:11 PM #

      Hello – Synacor is not releasing certified binaries for Zimbra 9 (as we have done for Zimbra 8.8.15). Anyone with a GitHub account can build Zimbra 9 binaries and packages from the public FOSS repositories. See for details.

  2. ivan bishop May 22, 2020 at 12:03 AM #

    You have not answered my email on prcing for 1-5 mailboxes for sites that are educational in nature (non commercial).

    What are you ofgerng for 1 -3 license terms for LOW use, non profit groups or are you not

    Ivan FOSS 8.8.15 ;)

    • Gayle Billat June 4, 2020 at 11:03 PM #

      Hi Ivan – please email and let them know where you are located … so we can connect you with the right person. Thank you.

  3. Michael Kakuschky August 2, 2020 at 4:32 PM #

    What means Zimbra OpenSource comes without modern UI?

    Is there no web interface included in the OpenSource edition?

    • Gayle Billat August 24, 2020 at 8:02 PM #

      Hello Michael – you can download an open source version of Zimbra with the Classic Zimbra UI.

  4. Kevin October 30, 2020 at 6:34 PM #

    How do we upgrade from OSE 8.8.15 to version 9 .. will there be instructions in GIT ?

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