What it means
An email mask, such as a Firefox Relay address, forwards mail to a real inbox while hiding that inbox from a signup service. A throwaway inbox is usually a separate mailbox intended for short-lived use. If the masked address is your account username, you may need it for password recovery months later.
A real-world example
A shop account uses a unique Relay mask. Promotional mail can be paused for that mask, but deleting it before changing the shop's login could prevent receipt of a future reset message.
What to do
Label each mask and keep it in your password manager. Before disabling or deleting one, update the underlying account's contact address and test recovery.
The distinction that matters
Masks improve address privacy but do not prove a service is trustworthy or replace strong authentication. Mozilla advises using them mainly for lower-trust signups rather than critical identity and attachment-dependent communication.
Mozilla's Relay usage guidance
