Multiple SSL Certificates, Server Name Indication (SNI) for HTTPS

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Multiple SSL Certificates, Server Name Indication (SNI) for HTTPS

   KB 22637        Last updated on 2016-05-3  

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Note: This feature will not enable SSL Certificate for IMAP/POP or smtps connections. RFE #103362

Server Name Indication (SNI) is an extension to the TLS computer networking protocol by which a client indicates which hostname it is attempting to connect to at the start of the handshaking process. This allows a server to present multiple certificates on the same IP address and TCP port number and hence allows multiple secure (HTTPS) websites (or any other Service over TLS) to be served off the same IP address without requiring all those sites to use the same certificate. It is the conceptual equivalent to HTTP/1.1 name-based virtual hosting, but for HTTPS. The desired hostname is not encrypted, so an eavesdropper can see which site is being requested.

To make SNI useful, as with any protocol, the vast majority of visitors must use web browsers that implement it. Users whose browsers do not implement SNI are presented with a default certificate and hence are likely to receive certificate warnings. Source:Wikipedia

Getting Started

Zimbra Collaboration supports SSL SNI starting at 8.7 Release and requires always the Proxy service, which is required by Zimbra Collaboration 8.7 anyways. Zimbra-ssl-sni-001.png


  • Zimbra proxy service must be installed and enabled on the server. In multi server environment, follow these steps on the proxy node
  • You should have a signed certificate + matching key pair and the trusted chain certs from your CA (Certificate Authority) (This is a common issue, so please, make sure you check your files before deploy the files)
  • You can bind Multiple SSL Certificates to just one ipv4 addresses, which will pair to the respective domain name. For example: =>>

and you could even have another IPv4, for Customer reasons with other group of SSL Certificates, even different type of SSL Certificates: => (A Comodo Wildcard SSL Certificate) => (A free Let's Encrypt SSL Certificate) => (A RapidSSL Certificate)

Browser support for SNI

The following browsers do offer support for SNI, however Zimbra hasn't tested all of them, it will be responsibility of the web-browser, to support the application part of SNI  :

Software Type Supported Notes Supported since
Internet Explorer Web browser Since version 7 on Vista (not supported on XP) 2006
Mozilla Firefox Web browser Since version 2.0 Reference 116169 2006
curl Command-line tool and library Since version 7.18.1 2008
Safari Web browser Not supported on XP
Google Chrome Web browser Since 6.0 2010
BlackBerry OS Web browser 7.2 or later
Windows Mobile Web browser Some time after 6.5<ref>Template:Cite web</ref>
Android default browser Web browser Honeycomb (3.x) for tablets and Ice Cream Sandwich (4.x) for phones<ref>Template:Cite web</ref> 2011
wget Command-line tool Since version 1.14 2012
Nokia Browser for Symbian Web browser
Opera Mobile Web browser Not supported on Series60

Configuring the IP address per domain

  • 1. Add the new domain, in this case Set zimbraVirtualHostName to and zimbraVirtualIPAddress to Make sure the zimbraVirtualHostName is set to the name which will be used to access the domain (URL) and the SSL certificate is signed for same name.
 zmprov md zimbraVirtualHostName zimbraVirtualIPAddress

NOTE: If the server is behind firewall and NAT'ed with external address, make sure the external requests for "" hits the aliased IP address and not the actual local IP of server.

Verifying and Preparing the Certificates

We should have three files received from the CA (might variate depending on the Certificate Authority). The server (domain) certificate, two chain certs. And we have existing key file (which was used to generate the csr)

  • 1. Save the certificate, key and chain files to a directory /tmp/ You can receive single or multiple chain certs from your CA. Here we have two chain certs from the CA. i.e. and
 ls /tmp/
  • 2. Add the chain certs to a single file called example.com_ca.crt
 cat >> example.com_ca.crt
  • 3. Confirm if the key and certificate matches and chain certs completes the trust. As zimbra user:
 /opt/zimbra/bin/zmcertmgr verifycrt comm /tmp/ /tmp/ /tmp/

    • Check the output, it should say something like this. If not, make sure you have correct key and chain cert files.
** Verifying '/tmp/' against '/tmp/'
Certificate '/tmp/' and private key '/tmp/' match.
** Verifying '/tmp/' against '/tmp/example.com_ca.crt'
Valid certificate chain: /tmp/ OK

Deploying the Certificate or Certificates on domain

  • 1. Add the domain certificate and chain files to a single file called
 cat example.com_ca.crt >>
  • 2. Run following to save the certificates and key in ldap database, as zimbra user:
 /opt/zimbra/libexec/zmdomaincertmgr savecrt
** Saving domain config key zimbraSSLCertificate...done.
** Saving domain config key zimbraSSLPrivateKey...done.
    • The syntax is:
 /opt/zimbra/libexec/zmdomaincertmgr savecrt <domainname> <certificate with chain certs> <keyfile>
  • 3. Run following to deploy the domain certificate. This will save the certificate and key as /opt/zimbra/conf/domaincerts/ , as zimbra user:
 /opt/zimbra/libexec/zmdomaincertmgr deploycrts
** Deploying cert for

Proxy Check

Run these commands on proxy hosts, or on the server if it's Single Server:

  • zimbraReverseProxySNIEnabled should be set to TRUE in server and global config.
zmprov mcf zimbraReverseProxySNIEnabled TRUE

Re-write and restart Proxy

  • Restart the proxy to re-write the changes to proxy config
 zmproxyctl restart
  • Once the restart is successfull, try to access the domain using the URL which is set in "zimbraVirtualHostName" over https. And check the certificate loaded in the browser. In this case the URL will be


You can go now to a Web browser and check the different zimbraVirtualHostName, and you will see that they will present to you different SSL certificates, the corresponding one per each virtualhostname.


  • If you do not see domain cert by accessing the domain with its zimbraVirtualHostName ( Make sure the https connection from Internet/intranet is going to server's local IP address which is defined in zimbraVirtualIPAddress, and make sure you have activated zimbraReverseProxySNIEnabled to TRUE
  • If you are using multiple proxy servers or adding new proxy servers, make sure you copy all the contents of /opt/zimbra/conf/domaincerts/ among all proxy servers. Otherwise proxy service will fail to start.

Known Issues

Verified Against: Zimbra Collaboration Suite 8.7 Date Created: 03/05/2016
Article ID:,_Server_Name_Indication_(SNI)_for_HTTPS Date Modified: 2016-05-03

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Wiki/KB reviewed by Jorge SME2 Copyeditor Last edit by Jorge de la Cruz
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