You will be able to access data that has already been loaded but will need to go online to use all the app's features.
If you are logged into the app and have synced artworks from your database already, you will be able to continue to access the loaded content when your device goes offline.
While you are offline you can continue to draft emails from the app. These will be saved in your Mail app's outbox.
You will need to go back online to receive updates from your database and send emails.