iCloud has a great feature that allows you to generate unique aliases on the fly quickly and easily. For example when signing up for new services via the web browser on iOS, you can generate a new address with the click of a button.

Many years ago, before I started using iCloud Mail, I was running my own email server and had it set up to forward everything sent to any address on my domain to my inbox. The advantage was that I could invent random aliases any time I wanted and didn’t even need to do anything on the server for those emails to get delivered to my main inbox. The very big drawback as I soon experienced was that spammers would email a lot of different email addresses on my domain that never existed but because I was going catch-all, would also get delivered to my main inbox. They’d be all kinds of email addresses like joe@ or sales@ or what have you. So apparently they were guessing common addresses and because I was accepting everything I’d also get tons of spam.

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sdevonoes 6 hours ago | parent [-]

The downside of such iCloud aliases is that you cannot send emails from there (you can only reply to emails, and ofc receive emails)

	▲	QuantumNomad_ 5 hours ago \| parent [-]
		True, and there has been a time or two where that has been inconvenient for me as well. Initial account creation confirmation email, and maybe even some newsletters, were sent from noreply@ some domain. Responding to such an email address directly will likely either bounce or be silently dropped on their side, as indicated by them using noreply as the sender address. The website might say to email support@ their domain. But because like you point out iCloud alias addresses cannot be used as sender when composing a new message, and I don’t have any past received emails from that address, I can’t email them using the same alias email address that I used to create an account. And of course if the account belongs to jumping.carrot-1j@icloud.com and I instead send an email to them from a different sender address, then they will be sceptical about whether it really is the account owner trying to get in touch or some impostor. Assuming they don’t completely ignore the email on that grounds, you might eventually get support if you are able to either answer questions from them about past invoice amounts and dates or similar, or if they are willing to email the original account owner address from their support address. But it’s extra hassle, if they even bother to respond at all. Fortunately most websites have a contact form or similar to get in touch with their support, but there are a few sites that have an email address as the only way to contact their support.