Send to Dropbox - Email attachments to a Dropbox folder
Polymail - Native email app for email productivity.
Get My Receipts by cloudHQ - Organize your receipts in one click
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.
OneBox.io - Sync e-mail attachments to GDrive, Dropbox, Box, or OneDrive
Morning Mail - A new way to manage your mail. Tinder for email.