[Galaco]

iCloud Custom Domains & Mail are filled with bugs. My favourite one is that if my custom email I want to register has EVER been associated with an Apple account, it can never be used as a custom domain, unless that domain is set to catch all; it is impossible to add that specific address; it just errors without any specific message. The original account was fully deleted; going to the arduous process they set up that takes weeks to actually delete the account.

Customer support is worthless for actual technical problems as usual for Apple. Fun extra regarding customer support; if you arrange a support call in a language not native to your region, they honor that, but that information is lost if they escalate the call; the callback is always in the national language, despite explicit requests over the phone during the callback schedule

[CraigRood]

For what it's worth, I was able to add my custom domain to iCloud under this exact scenario without any issues. This was 3 years ago, so I don't know if anything has changed, and I didn't have the 'catch all' limitation either.