Three DNS records decide whether receiving servers believe your email is really from you. Missing them doesn’t make delivery impossible — it makes your domain forgeable, and filters treat forgeable senders accordingly.
SPF — who may send
A TXT record listing the servers authorized to send mail for your domain (your mail host, your marketing platform). One record per domain; multiple senders share it via include: entries. The classic mistake is adding a second SPF record instead of extending the first — that invalidates both.
DKIM — proof it wasn’t altered
Your sending service signs each message cryptographically; the public key lives in your DNS. Receivers verify the signature. Each sending platform provides its own DKIM record — add every one you actually send through.
DMARC — the policy that makes them count
DMARC tells receivers what to do when SPF/DKIM fail: p=none (just report), p=quarantine (spam-folder it), p=reject (refuse it). Our recommendation: start at p=none to collect reports, confirm every legitimate sender passes, then move to quarantine or reject — a p=none left forever is a smoke detector with no batteries, and bulk-sender rules at the big providers now expect DMARC on any domain sending volume.
Verify all three in one shot with the deliverability checker.