What blocking throwaways reveals
An address is requested to make accounts cost something. A disposable address costs nothing, so it restores the situation the request was meant to prevent. A service that blocks them has told you the address was for limiting accounts rather than for contacting you.
The block feels arbitrary, and it is consistent with the purpose. Reading it as a signal rather than as an obstacle explains a lot about what a sign-up form is for.
On this page
The block follows from the purpose
If the address existed to reach you, a throwaway would be your problem rather than the service's. Blocking it means the address existed to make accounts scarce. That is a coherent goal and it is not the goal stated on the form.
How the block works
Lists of known throwaway domains circulate and are checked at sign-up. The lists are always behind, which is why some throwaways work and others do not, and why the same domain works today and fails next month. Nothing about your address changed; the list did.
The escalation
When throwaways get through, the next step is usually a phone number, because numbers are harder to obtain. Each step raises the cost of a fake account and raises the cost to everybody else by the same amount. The escalation is visible across the industry and it moves in 1 direction.
The alternative that ends it
A service that needs no account has no sign-up to defend, so no list, no number and no escalation. That is a design choice with its own trade-offs: no history across devices and no recovery. It is worth naming the trade rather than presenting it as pure gain.
Questions before you start
Is using a throwaway against the rules?
Often it is against the terms, which is separate from whether it works. Reading the terms is the way to know, and most people never do.
Do aliases from a mail provider get blocked?
Less often, because they resolve to a real mailbox at a known provider. They keep the join weak while staying acceptable.
Why not just allow them?
Because bulk accounts are a real cost to a service. The argument is not fake, and it is also not the same argument as the wording printed next to the field.
Open a chat with no sign-up to defend and no list to be on.
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