To add a new domain to your Zimbra server, log into your admin control panel at https://xxx.yyy.zzz.aaa:7071
Once logged in, click on the "Domains" link from the left navigation bar and then click the "New" link at the top of the panel on the right hand side.
Enter the new domain name in the "Domain Name:" section and again in the "Public service host name:" section. Enable the domain by selecting the "Domain status" state and hit the Next button three times until you get to the Virtual Host section. Enter something like webmial.yourdomain.com if you plan on allowing your users webmail access. If not, just click the Finish button to add the domain.
Now you need to add user accounts. Click the "Accounts" link in the left navigation menu and add your new users and their passwords.
After all your users are added, update your DNS zonefile for the domain you just added. So, if you had entered yourdomain.com into the Zimbra system, you would change the yourdomain.com zonefile's MX record to point to mail.yourdomain.com (if it isn't already). Then add an "A" record for mail.yourdomain.com to point to the IP address of the Zimbra server. If you added a hostname like webmail.yourdomain.com to the Virtual Host section when you added this new domain, create another "A" record in your DNS zonefile to point to the IP address of the Zimbra server so your clients can login via http://webmail.yourdomain.com
You would now configure your email clients just as you have done so in the past or reference our Outlook configuration