In Pictures: 15 Chrome OS productivity apps that w...
Gmail Offline lets you read and write emails offline and then automatically exchange them when you're online.
The app caches your list of contacts so you can address and write emails while disconnected. Gmail Offline lists unread emails on the left and shows the active item's contents on the right; it displays a contact's image when one is available and (like Gmail) defaults to a pastel-colored icon otherwise. The app is currently in beta, but worked fine for me during two weeks of daily use.
Gmail Offline doesn't allow you to embed an image in an email, although you can attach it. That being said, the app is useful for getting emails written when you're on the road.
In Pictures: 15 Chrome OS productivity apps that work offline