iOS 15.4 beta adds support for setting up custom email domains with iCloud Mailsource • macrumors.com
The iOS 15.4 beta that was introduced today expands support for the custom email domain feature available for iCloud+, adding an option to set up a custom domain with iCloud Mail directly on the iPhone.
I don’t see myself needing this feature necessarily since this service has been set it and forget it for me, but glad to see it there for setup. I added three domains while iOS 15 was still in beta over the summer and experienced zero issues. The killer feature for me is push mail notification support for a custom domain. No need to jump into the Mail app to refresh IMAP when receiving a 2FA code or similar.