The parent comment referred to "every" recipient knowing ones email address and "anyone who has hacked those recipients". The idea seems to be that all email addresses become "public". But this seems to assume things about the user and how they use the email address.

What if a user has an email address that she does not use to send mail? She does not use this account to send mail. She does not need to send reply mail. She has other email accounts she can use if she needs to send mail. If she only shares this address with one sender, then is this not at least a "semi-private" email address?

Back in the early 1990s when email accounts started to become easy to obtain, I routinely had accounts where I only received mail. I only gave these addresses to one or a few senders. I did not use these accounts to send mail.

I do not use email as avidly as I did back then, and maybe things have changed, but I would be a little surprised if today when a user sets up a new email account she starts immediately getting email1 because "all email addresses are public", before she has given this address to anyone. The address is "semi-private" unless and until the user decides to disclose it widely. She may choose not to do that.

1 Except maybe a welcome email from an email provider.