It logs onto the server and reads the headers of all the mail. It checks the subjects against it's "likely to be spam" parameters and any filters you have constructed for it. It compares the from address against friends and foes lists.

It displays a list of all the items it doesn't have a clear delete decision for showing from address, subject and its recommendations. You can review the list, make any changes you want by checking boxes, and recommend addresses to the friend/foe lists. It will then delete all unwanted mail from the server and call up your mail reader to download all that remains.

The mail reader I use, PMMail, allows you to log onto the server, review what's there and mark it for delete, retrieve or retrieve copy, but it doesn't have the decision engine so you have to look at the whole list. One of my clients is using MailWasher Pro as a preprocessor for PMMail.