Thank you thank you uxbod, you are a lifesaver problem solved. It's a lot easier than I thought - I can access email accounts again.

Actually for years I used to run qmail and was used to installing ssl certs no problem via CLI, and I've only been using zimbra for a year or two so this is the first time I actually tried installing the mail server cert under zimbra, it's actually much easier than my old method.

Thanks very much!