Google has updated their Offline Gmail app for Google Chrome with some user selectable options.
You can now select the time period for while the app would cache the mails locally. You can select from 1 week, 2 week and 1 month options.
There is also a vacation responder available.
Improved attachments: All attachments are now downloaded and available for offline use
Keyboard shortcuts support: If you have keyboard shortcuts enabled in Gmail, your setting will transfer over to the Gmail offline app. If you’re not sure what you can do with keyboard shortcuts, try pressing ‘?’ next time you’re using Gmail or Gmail offline.
Numerous performance enhancements: Messages and attachments now download at a faster rate and some bugs have been fixed.