With an iCloud+ subscription, you can use your own domain with iCloud Mail.
- Sign in at icloud.com, open Account Settings and find Custom Email Domain.
- Click Manage, choose who will use the domain and enter it.
- Apple shows the DNS records you need: MX records, a TXT verification record, an SPF TXT record and a DKIM CNAME record.
- In cPanel, set Email Routing for the domain to Remote Mail Exchanger.
- In Zone Editor, remove the existing MX records and add each record exactly as Apple shows them. If you already have an SPF record, edit it rather than adding a second one.
- Return to iCloud and finish set-up.
Apple's verification can take a while after DNS changes; if it fails, wait an hour and try again.