It depends on your mail flow.
When the mail leaves our platform, where does it first go? Your email administrator should be able to answer this question if you are unsure. We can query your MX (Mail eXchange) records to see the first ‘hop.’ After that, we have no visibility into your environment, so your email administrator will be key to getting things safe listed correctly.
If your mail flow looks like this, you can follow the steps below in the link.
More detailed information found at this link.