ios mail how to send from custom domain

Hello DavidCameron1075,

It sounds like you already have iCloud Mail set up on your device, but there are some additional settings you'll want to check as well. You can find them in Set up a custom email domain with iCloud Mail on iPhone.

"Add a custom email domain to iCloud Mail

You can add a custom email domain you already own to iCloud Mail, or buy a new one.

Note: You need to have a primary iCloud Mail address before you can add a custom email domain on iPhone. See Create a primary email address for iCloud Mail in the iCloud User Guide.

1. Go to Settings  > [your name] > iCloud > iCloud Mail, then make sure “Use on this iPhone” is turned on.
2. Tap Custom Email Domain, then tap one of the following:
   1. Buy a Domain: Choose this option if you don’t yet have a custom domain. After you purchase it, you can create custom email addresses.
   2. Use a Domain You Own: Choose this option if you already have a domain, and you want to use it with iCloud Mail. You can configure email addresses you already have at that domain, and create more.
3. Follow the onscreen instructions.

If you’re adding a domain you already own, some registrars require you to change DNS records to set up your domain. See the Apple Support article Set up an existing domain with iCloud Mail."

If you're still unable to send emails using your custom domain after following the instructions, please contact Apple Support.

Take care.