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Zimbra Collaboration, formerly known as the Zimbra Collaboration Suite before 2019, is a collaborative software suite that includes an email server and a web client. It is a dedicated server that manages all of the mailbox contents, including messages, contacts, calendar, and attachments.
Messages are received from the Zimbra MTA server and then passed through any filters that have been created. Messages are then indexed and deposited into the correct mailbox.
This written guide will show you how you can secure your Zimbra mail server by successfully installing an SSL Certificate.

Step 1. Generating a CSR and Private Key

1: Head over to and login to your Zimbra Mail Server's Admin Portal

2: In the main menu, click on Configure.


3: Select Certificates and then click on the gear icon on the top right (next to Help) and select Install Certificate.


4: Select your Target Server and click on Next


5: Choose the Generate CSR option and click on Next.


6: Fill in the CSR Details as specified below:-


Country Name (2 letter code) [AU]: Type in the 2 letter abbreviation for your country.
State or Province Name (full name) [Some-State]: Full name of the state
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Locality Name (eg, city) []: Complete name of the city, no abbreviations
Organization Name (eg, company) [Internet Widgits Pty Ltd]: If you are a business; Enter your legal entity name. If you're not a business, any value entered will not be used in your certificate.
Organizational Unit Name (eg, section) []: If you are a business; Write the appropriate division of your company. It is best to use something generic such as "IT".
Common Name (e.g. server FQDN or YOUR name) []: Enter your domain name
Email Address []: Enter your email address

Now, select the required root length and click on Next to generate your CSR.

You will now see your newly generated Private Key and CSR. Make sure to store both in a safe location as you will need them for further SSL Configuration.

Step 2. Order and Configure the SSL Certificate

Now we need to order an SSL Certificate. If you visit our SSL Certificates List page, you will have a selection of Certificates you can order. If you have a simple website wanting to secure the one domain, you will be fine to use a Comodo PositiveSSL . If you are a business website you may want to look at using a Business SSL, we recommend a Thawte SSL such as the Thawte Web Server SSL Flexi.
If you require any assistance with selecting an SSL Certificate, please feel free to contact our sales team and they will be happy to assist.

1: Order the SSL and complete the checkout.

2: Once you have completed the SSL Certificate Purchase you can begin the configuration process. This can be started by going into your SSLTrust account and managing your recent purchase.

manage ssl

You then will need to click the Submit Configuration button to begin the configuration process.

submit ssl configuration

3: You now need to paste in the CSR you generated using the OpenSSL library in the Ubuntu CLI. This includes the lines:

configure SSL

Select Other for your Web Server Type.

ssl admin details

You will need to also enter the Site Administrator Contact Information.

This information is to be of the individual who is responsible to approve and SSL Certificate. If it is a business SSL, it needs to be a contact under the business.

The Technical Contact Information is the details of the individual responsible for the installation and management of the Certificate.
If you have ordered a business SSL, you will also be required to enter your business details. These should be the correct address and phone number and legal entity name. They will be required to be validated by the Certificate Authority, any mistakes will cause delays. More information on Business Validation can be found here.

4: Click Continue to go to the next Step. Here you need to select the Authentication Method to validate your domain name. This is required to prove you own the domain name and have permission to issue an SSL Certificate for the domain.

select domain validation method

Select the method that will be the easiest for you to use; File-Based Authentication ( HTTP / HTTPS ), CNAME Based Authentication ( DNS ) or Certificate Approver Email.

If you have access to one of the listed emails, this can be the quickest method

Click Continue/Submit to finish the Configuration process.

After you complete the domain validation via your selected method, your SSL will be issued. If you ordered a Business SSL, you will need to wait for the Certificate Authority to complete the Business address and phone validation. If the validation has not progressed, or you have not received your Certificate after some time, please contact our support team so we can check on its status.

sectigo validation manager

Step 3: Select the Target Server & Install the SSL Certificate

When your SSL Certificate has been issued, you will be emailed the Certificate Directly from the Certificate Authority. You can also download it from your SSLTrust Portal. Downloading it from the SSLTrust Portal is a good option as we format the certificate in an easy to use way.

Again; View your certificate management page within SSLTrust

manage ssl

1: Click on the Manage button and collect/download your certificate.

download ssl button

2: Select the format as individual files with either a .pem or .cer extension and click on Download Certificate.


3: Go back to the Zimbra SSL Installation dialog box and again choose the Installation option as Install the commercially signed certificate


4: Review the CSR which you generated and click on Next.


5: Upload the certificate files to your server and click on Install


Note:- If you get this error (error : system failure: exception executing command: zmcertmgr verifycrtchain).
This means that Zimbra was not able to automatically verify and deploy your certificates and you will have to do it manually.

To get rid of this error, simply execute the following steps:-

1: Create a certificate chain:-

You can do this 2 ways:-

a: Copy and paste the main certificate file, the intermediate files and the root certificate into one file and upload it to your server.


b: Run the following command.

cat path-to-certificate.crt path-to-intermediate-certificate/s.crt path-to-root-certificate.crt > path-to-chain-certificate.crt

Make sure to replace the command with appropriate paths. You can set a new output directory as a path for the chain certificate.

2: Verify the certificates:

/opt/zimbra/bin/zmcertmgr verifycrt comm path-to-private-key.key path-to-certificate.crt path-to-certificate-chain.crt

Generally, the command should look like this-

/opt/zimbra/bin/zmcertmgr verifycrt comm /opt/zimbra/ssl/zimbra/commercial/commercial.key /tmp/commercial.crt /tmp/ca_chain.crt

3: Deploy the Certificates

/opt/zimbra/bin/zmcertmgr deploycrt comm path-to-certificate.crt path-to-certificate-chain.crt

4: To finish, verify the certificate was deployed.

/opt/zimbra/bin/zmcertmgr viewdeployedcrt

Step 4: Restart your Server via the CLI

Once you've successfully uploaded the certificate files to your server and installed the certificate, it is now time to restart the server. To do so,
you will have to get root access to your server via SSH and execute the following commands:-

    sudo su
su zimbra
zmcontrol restart

That is it, you have successfully installed an SSL Certificate on your Zimbra Mail Server.

Step 5. Check the SSL is working

It is a good idea to go to your website and see if it works via We also recommend you use this tool to check the install has been completed successfully:

A2 Hosting SSLLabs A RatingYou may need to get your web developer, or update your website yourself, to make sure all files use https:// and all links to your site and within your website use https://
If you require any assistance with your SSL Installation please contact our friendly support team.

Further Configuration

1: Turn of older versions of TLS:-

  su zimbra
  zmprov mcf -zimbraReverseProxySSLProtocols TLSv1
  zmprov mcf -zimbraReverseProxySSLProtocols TLSv1.1
  zmcontrol restart

Author: Siddiqui Ammar

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