To try out the calendar synchronization users need to be on the new Yahoo Calendar Beta.

The Yahoo Mail Blog explains. "After you have installed or updated your Zimbra software, go to the Account Setup link and then look for the link to Edit your account details." 

"You should see a whole bunch of fun Synchronization Settings to select.  Just like the first time you set up your Zimbra, it should take some time to populate.  But once it finishes the first sync it should be much faster."

Yahoo says it has received frequent comments from users who wanted a way to synchronize their Yahoo Contacts and Calendar with Zimbra.

If users have problems they can visit the Zimbra Desktop forums to offer feedback or report issues.