It would be great to be able to define how many days of previous messages you want synced (online and offline) on the mobile app.

E.g. sync 5 days, 15 days, 30 days, 3 months, 6 moths, 1 year, all mail

This is very useful not only to save storage space (on shorter syncing periods), but also for travels and offline searches (on longer periods).

Thanks!