As a first step, I suggest reviewing the article I mentioned earlier and following the instructions provided. Additionally, verify if your DKIM is properly connected and utilize this tool to check for any SPF errors
If you encounter an error after following those steps, I suggest reaching out to HubSpot Technical Support. Support is included in your subscription, and they can offer real-time assistance on this issue. You can share screenshots and provide additional information to help them address the issue effectively.