App Name: K-9mail
Description: “K-9 Mail is an open source email client focused on making it easy to chew through large volumes of email” (from their wiki page). K-9 is one of numerous email clients for Android. It contains numerous features such as POP3, IMAP, Exchange 2003/2007, new mail notifications, signatures, multi-accounts. You can save emails to SD and manage your various email accounts via your Android device.
Cost: Free, open source
Developer: K-9 Dog Walkers
Excellent K-9 mail app for Android keeps your messages on a leash – ARS Technica
K9 Mail – Android Tapp
MKB Reviews: K-9 Mail (video) -DroidDog
K9 Mail Android App Review (video) – Hemorrdroidsnet