So here is the explanation of what these three elements are, and how we should configure them to appear, even at a technical level, as "handsome as possible" in the face of anti-spam filters.

FIRST STEP: THE SPF

Sender Policy Framework (SPF) is an email validation system designed to prevent spam by detecting techniques commonly used by cybercriminals such as spoofing, a common vulnerability, by verifying the sender's IP address.