IMP 3 is the new stable version of IMP. Features that have been added
include searching; a new, flexible preferences system; a hierarchical
folder tree; and more.

It requires PHP4. You should use it if you want to take advantage of
PHP4s built-in session handling and improved speed or if you want access
to features such as the interactive spell checker and folder searching.

WWW: http://www.horde.org/imp/