Automator: save email attachment

I want to use Automator to select mail messages and then save the attachment in each message to a folder. The messages are in the same account, from the same sender, and have almost identical subject lines. I want it to run whenever I get a new message that meets the criteria (i.e. run in the background).

I've tried a workflow, an application, and a service. I've tried following guides others have posted. No matter what I try, each action results in the "the action...was not supplied with the required data".

I don't mind using Rules in Mail, but I don't want to use Applescript.

Can someone give me a walkthrough of how to do this that actually works?

Sierra 10.12.6, Automator 2.7