Three acronyms decide whether your mail lands in the inbox or the void. Here's what each one actually does.
SPF — the visitor list
SPF is a DNS record that says: “these servers, and only these, are allowed to send mail for my domain.” When a receiver gets a message, it checks the connecting server against the list. A server not on the list fails the check — and failures are strong spam signals. Keep the list tight: every server you add is a door you also have to watch.
DKIM — the wax seal
DKIM adds a cryptographic signature to each message. The public key lives in DNS; the receiver verifies the seal and knows two things: the message wasn't altered in transit, and the sender owns a key authorized for that domain. Unlike SPF, the signature survives forwarding — a letter with a wax seal stays sealed however many hands carry it.
DMARC — the referee
DMARC ties the other two together and answers the policy question: “if SPF and DKIM disagree with the visible sender, what should you do?” It has three answers — none (just report), quarantine (folder of shame), reject (drop it). It also sends you reports so you can see who is sending mail as your domain.
The one rule that matters
All three checks are about alignment: the pieces of a message's identity must agree with each other. A perfectly signed message whose signature domain doesn't match the From domain still scores badly. This is exactly why on JayWolfz Mail every outbound message is signed with your domain — the chain stays tight from relay to receiver.
Set all three, keep them aligned, warm up new domains slowly — and the inbox stops being a lottery.
— The deliverability team