Hmm… Confusing. I found the sent email - it was in my Gmail sent email box instead of the iCloud one. So it looks like it didn’t go through iCloud at all.
No, hide my email just assigns a random, unused iCloud.com email address as the sending and reply-to address for this message (plus I believe it can be re-used whenever you send to the same recipient), and when it receives a reply, the reply is re-sent to one of your Apple Account email address. See Create and manage Hide My Email addresses in Settings on iPhone - Apple Support - in particular,
Change which personal email address you forward to: Tap Forward To, then choose an email address. Options consist of addresses that are available with your Apple Account.
I don’t have an iCloud email address as my Apple Account and I can still use the feature, with replies that come back to my Fastmail account.
It let me set my main Gmail address (which is also my Apple account address and main address in Mail) as the forwarding address. But when I sent a test email from another address to the hide me address it didn’t arrive. And it’s not in junk.
And it looks like you can’t touch the forwarding address and change it.
I tried creating a new hidden address. I could not choose a forwarding address - it just set it to my Apple Account main address.
If I try turning off forwarding with a new test hidden address then email sent to that address can’t be delivered.
I guess I’ll contact Apple Support and ask. Just curious mainly. There was an article on CNET or someplace today about Google starting to offer hidden email addresses, so it got me curious.
Just to clarify, is your Fastmail account your Apple Account address? I don’t have an iCloud email address as my Apple Account either. I have a custom domain Gmail account for that.
If you create a hidden address does it always get set to forward to that Fastmail account with no choice?
Still, I wonder why if I send from an unrelated account to the hidden email address I created why it didn’t come to my Apple Account email address.
Inside the hide my email settings there is a place to set the forwarding address. That will forward all hide my email addresses to that address. The address must be an address you have set in your iCloud account.
If I send from my custom domain Gmail account to a hide my address address it doesn’t arrive. However, if I send from another non-Gmail vanilla SMTP account to the same address it arrives.
If the forwarding address is my Apple Account address (i.e. a custom domain Gmail account) then the sender address gets changed in the forwarding process to something that includes the sender address but has extra codey stuff added to it.
If the forwarding address is my iCloud email address then the sender address also gets “semi hidden” the same way. I can reply to that address though. Apparently Apple then handles forwarding in both directions.
But again, the forwarding process doesn’t work if the sender is a custom domain Gmail address. (I haven’t tried sending from a non-custom-domain Gmail address yet.)
Actually, that makes sense about the send address being “semi hidden” that way. It forces the email you reply to to go through iCloud and they protect you for accidentally revealing your actual address.
Anyway, interesting. I reported this to Apple support and they confirmed with screen sharing and they said it was odd about the sending from a Gmail account and asked me for more info if I find out more.