I have found the majority of these relay services utterly useless. A large number of sites are using some kind of email verification service/API that detect all these relay/trash domains (mailinator etc.) and you can never sign up unless you have a legit domain. I'd be astonished if mozmail.com wasn't already on this list.
I'm not saying I don't value the idea behind this, but at least with Apple they are using their primary domain as a relay meaning it's too risky to block all the legitimate addresses.
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