Final answer:
The button that a provider would select to restrict a proxy from viewing a message sent to the subject is the Encrypt button.
Step-by-step explanation:
The button that a provider would select to restrict a proxy from viewing a message sent to the subject is the Encrypt button.
When a message is encrypted, it is converted into a form that cannot be easily understood by anyone except the intended recipient. This ensures that even if a proxy intercepts the message, they will not be able to read its contents.
For example, in an email service, the provider may have an Encrypt button that the sender can select before sending a message. This will encrypt the message and prevent proxies from accessing its content.