You can recover past versions of your message. For example, you exit out of the email without saving. Similar to Microsoft Word, an auto-save version may be automatically saved for you if you were in the message long enough.
Accessing Restore Menu
Go in to the campaign you want to restore and click on "Utilities" next to the save button. Then click on the "restore" button in the drop down.
You can restore a previous version, both auto-saved and saved versions will be available.
You will also see a preview of the version you're recovering before restoring it. Once you've selected the version you want to recover, click "Restore" and the message will update with the restored version.