Everything mobile, Apple iOS and Google’s Android operating systems. Let’s face it, all other operating systems are insignificant.
So, you are heavily invested in the Apple echo system, and you are subscribed to iCloud+ for storage, music etc.
With the release of iOS 15.4, Apple has added the ability for users with paid iCloud+ plans to create custom email domains directly on their iPhone.
When you subscribe to iCloud+ (prices start at $0.99) you can use custom domains to send and receive email with iCloud Mail.