He responded because I re-forwarded the email in whole with my other teammate and boss all inside, even though he was already copied. He probably felt like I was throwing him under the bus since the whole team was in the thread. But I did it because he often ignored business emails and DMs, and I was the one getting heat from the business. I tried forward the email to only him but it took time to remove all parties and he also ignored it.
Complained to the boss before so I only forwarded subsequent business email, he uncharged of, to him while copy my boss as she asked me to do so since she wants to monitor the work. Then again, instead of backing me, my boss sided with him and questioned why I forwarded it again. I had to explain everything. She pretended to sympathize but then told me, “the whole team doesn’t like you forwarding emails when they’re already copied.” At that point, I was just like, whatever. They were not the ones constantly getting hounded by business for updates.
So I stopped forwarding anything to him or the team. When business came to me, I told them to reach out to the individual directly. Not long after, my boss brought it up in a meeting, asking why no one was monitoring emails or helping each other. That period was eye-opening, suddenly everyone became super alert to emails, only because no one else was doing the cover work anymore.