Integration with Sanebox Service
This may be a pretty big one. I see:
- Buttons to move messages to appropriate folders in the messages account, like @SaneLater, @SaneTomorrow, @SaneBackhole, etc...
- Unified views for Later, NoReplies, and Tomorrow between accounts.
I don't believe any other email client is doing this, so you might be able to get some love from Sanebox themselves. They might possibly tell all their Mac users that Airmail supports all the cool Sanebox features.
Evans Thompson commented
It seems to have died here, but the feature request is much more active on the iOS side.