PLEASE HELP - My Gmail inbox is not receiving emails from another person's Outlook

Hello,

I use Gmail for work, and my coworker uses Outlook for work. When my coworker says he's sent me something (to my Gmail email address) from his Outlook address, nothing populates my inbox. Not in spam, not in trash, not in any inbox. He is sending his emails to the correct Gmail address, and I am searching for his correct Outlook address. I do receive his emails when he sends them from his Gmail instead of his Outlook.

I've checked my blocked and forwarding settings, and there shouldn't be any issues (they're not blocked, and I'm not labeling received emails from Outlook to be forwarded/deleted).

Everything online is just talking about getting your Gmail to integrate/work with your Outlook. Nothing I'm finding is about person A's Gmail not receiving emails from Person B's Outlook. Before you say this is a Google issue, please let me know if there are any known compatibility issues/settings fixes from the Outlook side that my prevent his messages from sending to me.

Has anyone had this issue before? Any ideas of how to fix? I absolutely need to be able to receive emails from my coworker so I don't miss anything important.

Thank you,
Jake