Would like to say first that I love Zimbra and I have completely gotten rid of Exchange server and am using Google apps with Zimbra. It's AWESOME!!!
In Outlook, you could drag an email you received to the calendar and it would create a new appointment and copy the body of the email into the body of the appointment. I really miss this feature... The way I would envision it working in Zimbra is this:
1. Click and drag the email, move your cursor up to the "Calendar" tab.
2. The calendar tab opens and then wherever you release your email you are dragging, it will create an appointment on the time and day you release your click.
3. A new appointment pops up with the body of the email in the body of the appointment.
By the way, I'm not sure if this is the best place to post a feature request. Thanks for your time!