K9 is an experimental fork of the core Android POP/IMAP client. Primarily, K9 is focused on making it easy to chew through large volumes of email.

Release notes:

Improvements to “instant” delete functionality in folder/message list and message view – danapple0
Authentication method for WebDav(Exchange) changed. Support for non-Form Based Authentication. – ismarc31

http://code.google.com/p/k9mail/