A shop asks for an email address. You use a mask and its messages arrive in your usual inbox. That separation is useful, but the mask is another part of the delivery chain to remember.
Know where the message goes
A forwarding mask receives mail and passes it to another address. Mozilla Relay is one example. It can reduce the number of organisations that receive your primary address, and individual masks can help you identify which registration a message relates to.
The mask is not a separate, independent inbox unless the service explicitly provides one. Your ability to receive password resets still depends on the forwarding arrangement and destination account.
Record the address you registered
Save the exact mask alongside the corresponding account entry in your password manager. Otherwise, a later sign-in screen may leave you guessing which address you used.
Before relying on a mask, check a normal confirmation message and learn whether replies are supported. Do not infer those features from the fact that incoming mail works.
Close the account loop first
If you plan to disable a mask, review the accounts attached to it. Change their registered address and confirm the change before stopping forwarding, especially where email is used for recovery.
Continue using a unique password and the service’s available sign-in protections. A less exposed email address can be helpful, but it does not replace those controls or make the messages arriving through it trustworthy.