If you administer Zimbra on Ubuntu the following UFW profile may be of interest to you. For more information about UFW see https://help.ubuntu.com/community/UFW.

Create the file /etc/ufw/applications.d/zimbra with the following contents:

title=Zimbra Collaboration Server
description=Open source server for email, contacts, calendar, and more.
Enable the profile using:

sudo ufw allow Zimbra
sudo ufw enable
You can tweak the profile to meet your needs.