Postilion is a mail client with the NeXt look so should be of interest
to those using Window Maker and Afterstep. It is derived from tkRat, but
has some improvements in addition to the interface change.

Postilion uses virtual folders to map to your real mail hierarchy. This
can be a one-to-one or many-to-one mapping. Postilion has a couple
of features that are useful for mail archiving. One is "dynamic"
folders which will automatically store mail based on things such as
sender address or date. Another feature is the database. Mail can
be archived into a database which is handy for storage as well as
searching. Multiple virtual folders of type "database" can be setup with
different attributes. Any messages subsequently moved to these virtual
folders will be entered into the database with the attributes that were
specified for the respective folder. This can also be done on-the-fly
through a dialog box.

More information about Postilion can be found at:

http://www.postilion.org