The three records
SPF lists the servers allowed to send for your domain. DKIM adds a cryptographic signature that proves the message was not altered and came from you. DMARC tells receivers what to do when a message fails both aligned SPF and DKIM checks, and gives you reporting. Together they are table stakes for reaching the inbox.
Why it is non-negotiable now
Major mailbox providers have made authentication a requirement for bulk senders, not a nice-to-have. Missing or misconfigured records tank deliverability no matter how good your warmup or copy is. It is the first thing to fix before any cold campaign goes out.
Common questions
What do SPF, DKIM, and DMARC do?
SPF authorizes sending servers, DKIM signs the message to prove integrity and origin, and DMARC sets the policy for failures and provides reporting. All three are DNS records on your domain.
Is email authentication required?
For meaningful sending volume, effectively yes. Major providers now require authenticated mail, and unauthenticated cold outbound is routinely filtered or rejected.