Step #1: In Eudora, click on the Tools menu and select Filters.

Step #2: Choose to make new filter, using the New button in the bottom left.

Step #3:
In the Header drop-down box, select Subject:..
In the text box on the next line, type {SPAM?} or whatever other text you want the filter to find.
Then, in the Action drop-down box, select Transfer To and select the mailbox folder you want to move matching messages to (probably the Trash folder).

Repeat steps #2 and #3 for each filter you want to create. We recommend having one for {SPAM?} and one for {SPAM!}