Personally, I don't care what the guy does. It's entertainment for him, and obviously the people replying to his emails were entertained. I doubt they would continue to be entertained if more agents emailed them. I'm just pointing out issues with the article, why people might be upset.
Also, Hackernews tries to hold itself to a certain standard. Reading an article about an AI Engineer who gives an AI agent access to a tool, with clear directive and access to use the tool, who is then later confused when the agent uses the tool in a slightly different way, suggests the article is below Hackernews standards.
To answer your question though: yes you absolutely could fight spam with AI on your side.
Should we go down that path as a society, just for amusement? Essentially saying: yes, someone should pay for AI service to combat AI spam, just so we can continue to use email.