The iOS 15.4 beta, introduced yesterday, expands support for the custom email domain available in iCloud+ by adding an option that allows you to set it up on the iPhone.
If you are in the first preview In iOS 15.4, if you go to Settings -> Apple ID -> iCloud, iCloud Mail is now a tappable option and includes a section for setting up a custom email domain. Previously, custom domains could be set up using iCloud Mail, but not on the iPhone. This required visiting Apple's iCloud.com website. Setting up a custom email domain requires a paid iCloud+ storage plan, which starts at $0.99. This feature allows a custom email address such as john@appleseed.com to be used to send and receive emails using iCloud Mail. Even though the custom domain uses iCloud Mail, emails are addressed to and sent from the custom domain.
iOS 15.4 improves iCloud Mail
Any iCloud user can add up to five custom domains to iCloud Mail. Members of a Family Sharing group can also use that domain. Email addresses currently in use with the custom domain will be accepted, and there is also an option to set up new email addresses with the domain. The Custom Email Domain settings on iPhone and iPad make it much easier to use custom email addresses. The same feature is also available on Mac under System Preferences -> Apple ID -> iCloud Mail. However, it does not seem to be active yet. (Photo by Denys Prykhodov / Bigstockphoto)