SPF, DKIM, DMARC, warmup, and monitoring — everything you need to build bulletproof sending infrastructure and land in the inbox every time.
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Cold email infrastructure is the technical stack that determines whether your emails land in the inbox or the spam folder. It encompasses your domain setup, DNS records, sending platform, IP reputation, warmup process, and monitoring tools.
Most senders focus 90% of their energy on copy and sequences — but 70% of deliverability failures are infrastructure problems. No amount of great writing fixes a broken SPF record.
Your infrastructure has five core layers: 1. Domains — the sending identities you own 2. DNS Authentication — SPF, DKIM, DMARC records that prove you own those identities 3. Sending Platform — the software that sends mail and manages IPs 4. Warmup — the process of building IP/domain reputation before full volume 5. Monitoring — tracking deliverability health over time
SPF is a DNS TXT record that tells receiving servers which IP addresses are authorized to send email for your domain.
How to set it up:
1. Go to your domain registrar's DNS settings
2. Add a TXT record on your root domain (@)
3. Set the value to: v=spf1 include:yoursendingplatform.com ~all
Common SPF mistakes:
-all (hard fail) when you haven't tested all your sending sourcesCheck your SPF: Use mxtoolbox.com/spf or dmarcanalyzer.com to validate.
What each qualifier means:
+all — Dangerous: allows any server to send~all — Soft fail: suspicious servers accepted but marked-all — Hard fail: unauthorized servers rejected outright (best, once confirmed)DKIM adds a cryptographic signature to every email you send. Receiving servers verify the signature against a public key stored in your DNS. This proves the email wasn't modified in transit and actually came from your domain.
How to set it up:
1. Generate a DKIM key pair in your sending platform (most do this automatically)
2. Copy the public key they provide
3. Add it as a TXT record on your domain: selector._domainkey.yourdomain.com
Common DKIM mistakes:
Check your DKIM: Send an email to mail-tester.com or use mxtoolbox.com/dkim.
Selectors: Your sending platform may use multiple selectors (e.g., s1._domainkey, s2._domainkey). Add all of them.
DMARC tells receiving servers what to do when an email fails SPF or DKIM checks. It also enables you to receive reports showing who is sending email from your domain.
How to set it up:
Add a TXT record: _dmarc.yourdomain.com
Start with a monitor policy:
v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com; ruf=mailto:dmarc@yourdomain.com; pct=100
Then escalate to quarantine, then reject:
p=none — Monitor only, no action takenp=quarantine — Failing emails go to spamp=reject — Failing emails are blocked entirelyTimeline recommendation:
p=none + analyze reportsp=quarantinep=reject2024 Gmail Requirement: Gmail now requires a DMARC policy for anyone sending 5,000+ emails/day to Gmail addresses. p=none satisfies this requirement.
DMARC Report Analyzers: dmarcanalyzer.com, postmarkapp.com/dmarc, valimail.com
Warmup is the process of gradually increasing your sending volume from a new domain or IP address. Mailbox providers watch for sudden volume spikes — a brand new domain sending 1,000 emails on day one is a massive spam signal.
30-Day Warmup Schedule: | Week | Daily Volume per Inbox | |------|------------------------| | Week 1 | 10-20 emails | | Week 2 | 25-50 emails | | Week 3 | 50-100 emails | | Week 4 | 100-200 emails |
What warmup tools do: Services like Instantly.ai, Smartlead, and Mailreach send automated emails between real inboxes and mark them as "not spam" — building your reputation algorithmically.
Warmup rules:
Signs your warmup is going well:
Setting up your infrastructure is step one. Keeping it healthy is the ongoing work most senders ignore — until they hit a deliverability crisis.
Weekly checks:
Monthly checks:
Red flags to watch:
Tools for monitoring:
Check off each item before sending your first campaign from a new domain.