Is this the same as sending email from your domain? If so you can go to settings then emails & SMS. Very top option is outgoing email settings. Enter your email that is tied to the domain you want. Thats the easy part the hard part is you then need to login to your domain provider and add DKIM and SPF Value. I was able to get My SPF Value to Verify but Im stil stuck waiting for help on how to get the DKIM record to verify.