Because another company hosts your domain (your domain registrar or Web host provider), you'll need to fix it on their website. ...

Because another company hosts your domain (your domain registrar or Web host provider), you'll need to fix it on their website. There's nothing we can do to fix it on our end. We've created a tool that guides you step by step through the process.
Follow these steps to use the tool.
  1. In the Office 365 Admin center, go to the Manage domains page.
  2. Choose Fix issues next to the domain that you need to fix.
  3. Follow the instructions on the page for fixing your SPF record.