KK Mail

KK Mail is Based on K-9 Mail.it is focused on making it easy to chew through large volumes of email.

Its improved features include:

Push mail using IMAP IDLE
Better performance
Message refiling
Email signatures
Bcc-to-self
Folder subscriptions
All folder synchronization
Return-address configuration
Keyboard shortcuts
Better IMAP support
Saving attachments to SD
Empty Trash
Message sorting
...and more