* Log on to your server as root and go to the directory /opt/zimbra/ssl/zimbra/ca and run command :
openssl x509 -in ca.pem -out cacert.der -outform DER
* This will generate a file called cacert.der in the same directory. Copy this file and store it on the Windows system on which you want to import the certificate.
* Certificate import for Current User :
On the Windows client, do Start->Run->CertMgr.msc to access the Windows Certificate Store:
Right-click the Certificates folder under Trusted Root Certificate Authorities and choose All Tasks->Import. Follow the Wizard instructions to import cacert.der. Ensure that the certificate is placed in the Certificates folder under Trusted Root Certification Authorities.
* Certificate import for Local Machine :
Start mmc.exe (as administrator), menu File -> Add/Remove Snap-in.., select "Certificates", press Add, select radio button "Computer account", press Finish and OK.