Create User Accounts: Configure one account at a time, or migrate multiple existing accounts from a server.
Define Classes of Service: A default Class of Service (COS) is automatically created during the installation of Zimbra software. The COS controls mailbox quotas, message lifetime, password restrictions, attachment-blocking and server pools. You can modify the default COS and create new COSs to assign to accounts according to your group management policies.
Add Zimlets: Zimlets enable your end-users to look at information and interact with other third-party applications (calendar, maps, Salesforce.com, WebEx, and more) from within their email messages. Zimlets can be made available by modifying the Class of Service (COS).
Mail Queue Monitoring: Incoming and outgoing mail is processed by postfix in a series of queues that can be monitored from within the admin console; select Manage Mail Queues from the left sidebar and your queue information will be shown.
Certificates: Clicking Install Certificate from either the Manage Certificates tab or a Certificates tab opens the Certificate Installation Wizard. The Certificate Installation Wizard is a tool that will help you quickly create and deploy a certificate.
End-User Feature/Functionality Testing
Address Book: Importing/exporting contacts
Setting email preferences: Customizing signature files, text versus html
Consider a 60-Day free trial of Zimbra Network edition if you want email/phone support, mobile device sync, built-in archiving and compliance, or integrated unified communications. You can always easily go back to the free version, if you're not convinced.