Hi Kenmel,
From your post I understand that you are experiencing the email fail issue after you changed your website host.
Based on my experience this should be a DNS related issue, please confirm that you have added the correct MX record for Office 365.
In Office 365 Enterprise plan, login Office 365 admin center and click domains tab, choose your domain and click Troubleshoot, follow the wizard and check if it helps.
Additionally, you can send a test email to your Office 365 account from Hotmail or Gmail, if the email is rejected you will receive an NDR (Non Delivery Report). You can provide the NDR and help us troubleshoot this issue.
Thanks,
Bourne Zhang