Thunderbird
Setting up the SpamAssassin Filter
Create a Spam filter 
- Click on Tools
- From the drop down menu, choose Message Filters

- Click on the New button

- At the top, enter SpamAssassin in the Filter name box
- In the For incoming messages that section, click on the first dropdown box and choose Customize.

- Enter X-Spam-Flag in the "New Message Header" field
- Click Add
- Click Ok
- Now choose X-Spam-Flag from the first dropdown box.
- "Contains" should already be selected in the second dropdown box
- Type in the word YES (all in caps) in the third field

- In the Perform these actions section:
- Click the first dropdown box and select Set Junk Status to
- Junk should now automatically appear in the second dropdown box
- Click on the + sign to the right of this row
- Move Message to should automatically be selected in the first dropdown box in the second row.
- Select the Junk icon (the flame) located below the "Local Folders" entry in the second dropdown box of the second row.
- You will now see Junk on Local Folders listed in the second dropdown box of the second row.

- Click on OK
- You should now see "SpamAssassin" in the Enabled filters list.
- Exit the Message Filters window by clicking on the 'X' in the upper right hand corner.
- Exit Thunderbird by selecting the File menu option and then Exit.
A general guide to creating Thunderbird filters is covered in the document "How to create an email filter in Thunderbird". Use this document as a frame of reference if you want to redeploy some of the same types of filters in Thunderbird as you had in Eudora.