Using Classic Outlook on Windows for personal email, calendar, and contact management
Dear Jason Bootten,
Thank you for visiting Microsoft Community, I am glad to assist you here.
Based on your description, I understand you would figure out your email routing as it seems nowhere to find from recipient's side.
If you are able to run message trace in Microsoft 365 admin center, and the result only tells limit information, please try to run a Enhanced summary report, where you may find more details.
Normally if the status says delivery on Microsoft 365 side, it means the emails were delivered to recipient's server, and if there were actions on recipient's server side, you may probably have to ask your recipient to run such trace log from its side.
Hope this is helpful and please feel free to get back to us if you have further concerns,
Regards,
Microsoft Community