Does iCloud Custom Email Domain work with older operating systems?

Is iCloud's Custom Email Domain feature compatible with previous versions of macOS and iOS? Specifically, will I be able to send email using a custom email domain from a device running any old version of macOS or iOS?

Apple doesn't list any requirements that restrict Email Custom Domain to newer operating systems and the support page specifically says "Set up a custom email domain for iCloud Mail on all your devices"

https://support.apple.com/en-gb/guide/icloud/mm0e4339d289/1.0/icloud/1.0

But I want to double check because I'll be transferring gigabytes of email in the process, so I don't want to find out after that fact that it doesn't work with an old iMac I have. Also, during the beta stage of Custom Email Domain, I know it was limited to macOS 12 and iOS 15 at the time.