To fix this issue, contact the recipient's email admin and ask them to work with their domain registrar (or Web host provider) ...

To fix this issue, contact the recipient's email admin and ask them to work with their domain registrar (or Web host provider) to properly set up a correct MX and A record for their domain.

Only the recipient's email admin can fix this. Unfortunately, Office 365 support won't be able to help with these kinds of errors.