What is authentication (overview)?

Authentication verifies that a message truly comes from the domain it claims to represent. It relies on SPF, DKIM, and DMARC, which together create a chain of trust between the sender’s domain and the receiving server.

Think of it as showing stamped papers at every checkpoint in the harbor. The deeper purpose of authentication is non repudiation, which proves that a sender cannot deny sending a message that aligns with their domain. Without authentication, modern mailbox providers treat a message as suspicious by default.