Mozilla Thunderbird is an Open Source email client. It is free to use and has many features. It can be downloaded from http://www.mozilla.org/products/thunderbird/. To configure it to filter messages based on the X-Spam-Status header created by SpamAssassin, follow these directions.

From the File menu, select New and then Folder to create a new folder for filtering spam into. The application prompts for the folder name and also the parent folder. Enter an appropriate name and choose an appropriate parent folder. If an IMAP server is in use, then it is advised to store the spam folder on the server. This enables the email administrator to access the spam for Bayesian learning or for use as a corpus. After the name and parent have been chosen, click OK

Next, to define the filter, select Message Filters from the Tools menu. In the dialog box, click the New button.

In the next dialog box, enter a name for the filter, for example Spam. Then, select Match all of the following...