So far I’m singularly unimpressed by iCloud+ Custom Email Domains. Some 48 hours after I initiated the transfer, the domain still isn’t set up properly. Turns out not all the DNS records were set.
Thankfully this was with a domain I don’t use much. I’d be fuming if this happened with either of my primary domains!
Part of the problem, I suspect, is that Apple are trying to be helpful and automate as much of this as possible. Frankly, I would have preferred to just tick a box saying “I can handle this myself” and enter the new DNS records myself.
I don’t think I’ll be giving up or downgrading my current Fastmail service anytime soon — it may cost more, but the service and support match the price pretty well in my experience.