So the idea here is that when you “mark as spam” it doesn’t just bin it. A bot fires up, and actively manages that conversation such that you never see it, but it responds to the email, then tries to hold a long and drawn out conversation that ties up as much time as it possibly can of the spammers. It sets up all the relevant rules to move it to it’s own folder and acts on it from there.
The idea is simply to waste spammers time because now instead of spamming a million emails and getting 2 responses and working on scamming them, they now get a million emails back and have to spend time trying to work out which ones are bots and which ones are not.