Modern
The Modern Web App delivers a responsive experience across all your devices and integrates with many popular apps.

Classic
The Classic Web App is familiar to long-time Zimbra users. It delivers advanced collaboration and calendar features popular with power users on Desktop web browsers.

Default
This will sign you in according to your saved Preference. In the Modern Web App, set this preference in Settings > General > Zimbra Version. In Classic, set it in Preferences > General > Sign In.