An email address for signing up to a website
A site wants an address before it will show you anything. You want to look at it once. Those two facts are the whole problem, and the reason a category of throwaway-address services exists at all.
The cost of handing over your real address is not the one welcome email. It is that the address is now a key: it turns up in the site’s mailing list, in whatever list that company sells or loses, and in every breach database compiled from either. Addresses are the join column that lets otherwise unrelated leaks be assembled into one profile of a person.
What a throwaway address actually does
It gives the site something that behaves like an address — mail sent to it arrives — while being connected to nothing else you own. When you stop reading it, it stops mattering. There is no unsubscribing, because there was never anything to unsubscribe from.
What it does not do is hide you. The site still learns your IP, your browser, and whatever else you type into it. A throwaway address solves one problem well and no others.
The part every one of these services gets wrong
The address is the easy half. What actually costs you time is the next step: the site sends a code, and you have to open a mail client you do not care about, find the message, and read six digits out of a marketing template built by somebody who never imagined you would be looking for exactly one number in it.
SpareInbox reads the message for you. The code appears on the page, in large type, with a button that copies it. If the message is a confirmation link instead, the link appears as a button. You never open the email. More on getting the code without an inbox.
When not to use one
Anyone holding the address can read its mail — there is no password on it, and there cannot be, because you did not create an account. That makes it right for a forum you will visit once and wrong for anything you would need back:
- Never a bank, an exchange, or anything holding money.
- Never an account you intend to keep. Password resets go to the address on file, and this address will not exist in a month.
- Never anything you would mind a stranger reading, because a stranger might.
Some sites will refuse it
Signup forms keep lists of disposable-mail domains and reject addresses on them. This is not a bug in the service and it is not something to be indignant about — it is a site deciding it does not want single-use signups, which is its right.
When it happens the form usually says the address is invalid rather than blocked, which is confusing but not mysterious. Use your real address, or decide the site was not worth the signup. How disposable addresses work, and why they get blocked.