1. Login to Zimbra Webmail. Click on “Preference > Accounts > Add External Account" as shown in below.
2. After clicking above mentioned option give server information and user information to the below text boxes. Give email address which have to configure as a external mail account, Choose account type IMAP , give mail server (example: mail.domainname.com) and user login credentials. After giving all required details click on “Test Setting” button to confirm that whether all the settings are correct or not.
3. After complete all the steps which have shown above click on “Save” button.
4. Now your external email account inside Zimbra Webmail is ready to use.