Hi Jeannette,
According to your NDR, I resolved your domain name using the nslookup command-online tool, it indicates that you have redirected to Office 365 and the DNS records are correct.
For this situation, I recommend you to do the next steps:
1.Please send a test email to email address csa@warrclinic.co.uk by using other email addresses, such as Yahoo, Gmail, Hotmail , and check whether these email addresses can receive the same NDR as you post above.
2.You can ask for help from your administrator to check whether the sender address scryans@quadratek.net can send emails to csa@warrclinic.co.uk successfully.
Thanks,
Vivian Wang