Outlook on Android will connect to a Zimbra server using Exchange ActiveSync Protocol (EAP) :

Install Outlook from the Google Play Store and start the app.

If no accounts were previously configured: Tap Add Account.

If you are adding an additional account: Tap Settings

Fill in your entire email address and tap Continue.

Your phone will take a few seconds attempting to find your mail server/account. It may flash an option to setup manually and then it will go to this screen. Tap NOT OUTLOOK? then Change account provider.

Tap Exchange

Fill in your email account password and a descriptive name for the email account. Then slide the ADVANCED SETTINGS switch to the right.

Fill in Server with zimbra.virtualarchitects.com and Domain/Username with your entire email address. Tap the check mark in the upper right corner of the screen.

On this screen tap SKIP if you don't have another account you want to add right now.

You will have the opportunity to scroll through 3 pages of tutorials. You can do that then tap the check mark on the bottom right to finish or tap SKIP to avoid tutorials.

Once the account is added you may want to change a couple settings by tapping the gear icon in the upper right corner of the screen. I suggest modifying Notification, Signature and Focused Inbox to suit your needs.