Hi I am writing this how to because this is something that I have been attempting to do for quite some time, always unsuccessfull ... so when I got it to finaly work I wanted to share it with everyone.
This is a very easy way to get an SSL Certificate working with Zimbra.
1. Log into your Zimbra admin webpage.
2. Select "Certificate" on the button selections at the left on the screen.
3. Click on "Install Certificate" toward the top of the screen.
4. Select the server name you are getting the ssl certificate for and then next
5. Click on "Generate CSR for the commercial certificate authorizer" and then next
6. Take the defaults on this screen and select next
7. You are now posed with "Download the Certificate Signing Request screen"
8. Click on "download the CSR" and save this file to your desktop as current.csr
9. Goto RapidSSL which has FreeSSL so that you can try it for free first. Goto https://products.geotrust.com/orders...do?ref=freessl to get your free ssl certificate. During the process you will copy the text that makes up the file you just created current.csr and paste its contents into the RapidSSL / FreeSSL signup form (use your favorite text editor to do so). Once you have gone through the process at RapidSSL / FreeSSL you will receive an email with your certificate data.
10. Create a file called domain_ca.crt and paste the certificate data into it using your favorite text editor (make sure to include the ---- from the begining and again at the end).
11. Go back to your Zimbra admin webpage - certificates area.
12. Click on Install Certificate toward the top of the screen once again.
13. Take the defaults and click on the next button.
14. Click on Install the Commercially Signed Certificate and then Next
15. Take the defaults once again and click on next
16. Create a text file on your desktop named root_ca.crt and paste the following into it ...
17. Now save and close the file.
18. Click browse next to the Root area and locate the root_ca.crt file you just created select ok.
19. Click browse next to the Certificate area and locate the domain_ca.crt file you created earlier.
20. Click next and your home free. Complete the wizard and after you reboot your server you now have valid SSL certificates.