

I signed up with them ensuring I read their privacy policy. Based on my personal privacy threat model, I’m okay with their policy. This wouldn’t fit a more intensive threat model.
I haven’t read it recently but last I remember they do have the option to temporarily store an email in the event of a failed delivery, until it can eventually get sent to you. This is opt-in I believe, and a toggle you can enable in your account.
In the time I’ve used them I haven’t had any issues with email deliveries. Been happy with the service so far, having left SimpleLogin and Proton for political reasons.
When you get an email from Company A that sends to your alias email, the email goes to your inbox. When you reply to that email, your alias provider forwards it to Company A where the sender is your alias address.
In short, you simply reply and your alias service takes care of it for you so that the recipient only sees your alias email and not your true email.