• Go to Tools > Settings…
• For each mail account under Mail Accounts, click on the account name and click Edit. Go to the Receiving Mail pane. Change the host to 127.0.0.1, and the username to host:username. For example, if the host is furble.mail.com, and the username is jrbobdobbs, then the new host will be 127.0.0.1, and the new username will be furble.mail.com:jrbobdobbs. When this is complete, click OK.
• The first time you retrieve mail from your updated accounts, you will be prompted for your mail password again.

This worked under Evolution v1.4.0 - YMMV.

• Select Tools > Filters…
• Make sure Incoming is selected, and press Add
• Name the rule
• Select Specific Header for the criteria
• Enter X-Text-Classification in the box next to Specific Header (note there is no ':' after X-Text-Classification)
• Select Contains
• Enter spam in the box next to Contains
• Choose your action (I chose Delete which puts it into Trash).
• Save the rule.

That should work. Crtl+Y executes the rule against current messages if you want to test it.