K-9 is the best email client for Android

K-9 Mail

K-9 is the best email client for Android. It's incredibly powerful and 100% free

K-9 Mail is an open-source e-mail client with search, IMAP push email, multi-folder sync, flagging, filing, signatures, bcc-self, PGP, mail on SD & more!

K-9 supports IMAP, POP3 and Exchange 2003/2007 (with WebDAV).