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:

Add ability to “flag” messages – danapple0 Indicate which message have been replied to – danapple0 Fix links in plain text messages – danapple0 Improved synchronization timing – danapple0 Added support for pulling login URL for WebDAV login – ismarc31 Added default URL for mailbox path if path isn’t returned after WebDAV login – ismarc31

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