Open Door Technology

Follow the instructions in this video to setup your custom domain for use with your Office 365 Exchange Online:

1. In the Admin center, go to the Domains page, or choose Setup > Domains.

   
   

2. Choose Add domain.

Follow the instructions and video provided by Microsoft in the following link.

https://docs.microsoft.com/en-us/office365/admin/setup/add-domain?view=o365-worldwide