Chapter 4 of 8
Deliverability basics (SPF, DKIM, DMARC)
Deliverability is whether your email reaches the inbox instead of spam. SPF, DKIM, and DMARC are the DNS records that prove to receiving mail servers that you are who you say you are.
Why do SPF, DKIM, and DMARC exist?
Anyone can put any "from" address on an email — that's how spoofing and phishing work. SPF, DKIM, and DMARC are DNS-level records that let receiving mail servers (Gmail, Outlook, Yahoo) verify that a message claiming to be from your domain actually came from a server you authorized. Without them, your legitimate marketing email looks identical, to a spam filter, to a forged one.
SPF, DKIM, and DMARC, plainly
- SPF (Sender Policy Framework) — a DNS record listing which mail servers are allowed to send email for your domain. Receiving servers check the sending IP against this list.
- DKIM (DomainKeys Identified Mail) — a cryptographic signature added to each email's headers, verified against a public key published in your DNS. It proves the message wasn't altered in transit.
- DMARC (Domain-based Message Authentication, Reporting and Conformance) — a policy record that tells receiving servers what to do if a message fails SPF or DKIM (quarantine, reject, or do nothing), plus where to send reports about failures.
All three live in your domain's DNS settings, not inside your ESP's dashboard — though every ESP in the /tools database walks you through generating the exact records to add.
What happens without them
Gmail and Yahoo now require SPF and DKIM (and a DMARC policy) for any sender pushing meaningful volume, and messages that fail authentication are increasingly rejected outright rather than just flagged as spam. Even below that threshold, missing or misconfigured records raise your spam-complaint exposure and depress open rate simply because messages never arrive.
Warming up a new sending domain
A brand-new domain or IP has no sending reputation yet, so mailbox providers apply extra scrutiny. Warm-up means sending a gradually increasing volume — starting small, to your most engaged subscribers — over two to four weeks so mailbox providers can build a positive reputation profile before you send at full volume. See /glossary#warm-up and /glossary#sender-reputation.
Questions about deliverability basics (SPF, DKIM, DMARC)
Do I need SPF, DKIM, and DMARC for a small email list?
Yes. Major mailbox providers apply authentication checks regardless of list size, and skipping any of the three raises the odds of landing in spam even at low volume.
Does my ESP set up SPF and DKIM automatically?
Most ESPs generate the DKIM and SPF records for you, but you still have to manually add them to your domain's DNS settings — the ESP dashboard cannot edit DNS it doesn't control.
What's the difference between deliverability and delivery?
Delivery means the receiving server accepted the message; deliverability means it actually landed in the inbox rather than the spam folder. A message can be "delivered" and still never seen.