iCloud mail and private domain.
I just migrated my private domain mail accounts to iCloud Mail. I used my professional email address when signing up for the migration. After I migrated I couldn't find and send mail from my old mail address and when I try to set the address as a new entity iCloud says it's already in use by another Apple Account.
What have I done wrong? I'm getting the emails from the account but can't send them from the account. It wants to use an iCloud account instead. It may confuse my customers..
MacBook Pro 16″, macOS 15.1