Non-repudiation is the ability to prove that a message or document was sent or signed by a particular person, and that the person cannot deny sending or signing it. Non-repudiation can be achieved by using cryptographic techniques, such as hashing and digital signatures, that can verify the authenticity and integrity of the message or document. Non-repudiation can be useful for legal, financial, or contractual purposes, as it can provide evidence of the origin and content of the message or document.

Hashing ensures integrity of software by detecting any unauthorized changes or tampering after its final version.

An SPF (Sender Policy Framework) record needs to be updated to include the new email servers, allowing recipient systems to verify the legitimacy of the sending servers and prevent outgoing emails from being marked as spam.

Before applying any updates or patches to a production VM, especially one with a 99% uptime SLA, it is crucial to first take a snapshot of the VM. This snapshot serves as a backup that can be quickly restored in case the update causes any issues, ensuring that the system can be returned to its previous state without violating the SLA. This step mitigates risk and is a standard best practice in change management for critical systems.

Availability is the ability of a system or service to be accessible and usable when needed. For a web application that allows individuals to digitally report health emergencies, availability is the most important consideration during development, because any downtime or delay could have serious consequences for the health and safety of the users. The web application should be designed to handle high traffic, prevent denial-of-service attacks, and have backup and recovery plans in case of failures.