Offline mode is, quite simply, when your phone does not have internet access. Unlike the desktop web app, on the mobile apps you can also work without an internet connection.
For more information about using Office mobile apps at work, visit the mobile apps for business page. When users reconnect, Gmail automatically sends any outbound messages. Note that the maximum sync period for data is 30 days. Using the Gmail Offline Chrome app (recommended) Gmail Offline capability is provided as a free Chrome web application. Learn how to use the Gmail Offline Chrome app. Offline Gmail for your domain. To turn on Offline Gmail.