Cold Email Domain Setup Checklist: Everything Before You Send a Single Email

Most cold email deliverability problems start before the first email goes out. This is the exact domain setup checklist that prevents the most common infrastructure mistakes.

Why Domain Setup Determines Deliverability Before You Send Anything

Every deliverability problem I see in cold email operations traces back to a setup mistake. Not bad copy. Not a terrible offer. Not the wrong sending volume. A misconfigured SPF record. A missing DMARC policy. A domain bought last week and sent to 1,000 people on day three. These are the things that land you in spam, and they are all preventable.

This checklist is what I run through for every new cold email domain before a single sequence goes live. If you cannot check every box, do not start sending. Fix the setup first. The delay is worth it.

Domain Registration and Age

Use a separate domain for cold email, never your primary business domain. If a cold email domain gets flagged or blacklisted, your primary domain stays clean. This is not optional. Every outbound operation uses secondary domains. If your company is acme.com, your cold email domains look like getacme.com, triacme.com, meetacme.com. Register several and rotate them.

Domain age matters. Brand-new domains have zero sending history, which Google and Microsoft treat with suspicion. A domain registered yesterday and sending cold emails today has a higher spam placement rate than a domain with 30 days of warmup history. Buy domains 14 to 21 days before you plan to start campaigns, or use pre-warmed inboxes from Puzzle Inbox that arrive with established domain reputation.

Domain similarity to your primary brand. Use variations of your actual company name rather than completely unrelated domains. acme-sales.com looks more legitimate than randomwords123.net. The domain string itself is one signal among many that spam filters evaluate.

DNS Authentication: The Non-Negotiables

SPF record. Your SPF record tells receiving mail servers which IP addresses are authorized to send email on behalf of your domain. A missing or incorrectly configured SPF record causes a percentage of your emails to fail authentication checks. Check yours with MXToolbox. The record should exist, should include your sending provider's IPs, and should end in ~all or -all (not +all, which authorizes any server to send on your behalf).

DKIM signature. DKIM adds a cryptographic signature to every email you send that receiving servers use to verify the email actually came from your domain. Your sending provider (Google Workspace, Outlook 365) generates the DKIM keys. You add the public key as a TXT record in your DNS. Without DKIM, your emails are easier to spoof and spam filters treat them as less trustworthy. Verify DKIM is working with MXToolbox or the free DNS checker.

DMARC policy. DMARC tells receiving mail servers what to do when an email fails SPF or DKIM checks. A DMARC policy at p=none monitors failures without rejecting email. p=quarantine routes failures to spam. p=reject blocks failed emails entirely. For cold email, start with p=none to monitor without blocking, then move to p=quarantine after 30 days if your authentication is clean. A completely missing DMARC record is a yellow flag that some spam filters use as a negative signal. Add it even if you leave it at p=none for now.

Verify all three before sending. Run your domain through the DNS checker and confirm SPF, DKIM, and DMARC all show green. If any of the three are missing or misconfigured, fix them before campaigns start. A single misconfigured DNS record can drop your inbox placement by 15 to 20 percentage points.

Inbox Warmup: The Part Everyone Rushes

Minimum 14 days of warmup, 21 days is better. New inboxes have no sending history. Sending cold emails from a brand-new account before warmup is why people get 40% spam placement rates in week one. Warmup builds reputation by gradually increasing email volume with positive engagement signals. 14 days is the absolute minimum. 21 days produces meaningfully better inbox placement.

Pre-warmed inboxes skip this step. Puzzle Inbox pre-warmed Google Workspace and Outlook 365 inboxes arrive with the warmup already done. You can start campaigns within 24 to 72 hours of delivery. For teams who want to start sending immediately without a 2-week delay, pre-warmed inboxes are the right answer.

Do not stop warmup when campaigns start. Keep your warmup tool running alongside your active campaigns. The warmup signals counteract the spam complaints and unsubscribe signals that cold email generates naturally. Stopping warmup the moment you start sending is like taking the stabilizers off while still learning to ride. Run warmup and active campaigns simultaneously for the life of the inbox.

Volume Limits: The Math That Protects Your Domains

15 to 20 cold emails per inbox per day maximum. This is not a suggestion. It is the limit that keeps your inboxes healthy over time. Teams that push 50 or 100 per inbox per day burn domains faster and see spam placement rates climb within weeks. One inbox, 15 to 20 sends, period.

3 inboxes per domain maximum. More than 3 inboxes on a single domain creates too much concentration risk. If one inbox gets flagged, it pulls down the others on the same domain. Spread your sending across multiple domains.

Scale by adding domains and inboxes, not by pushing more per inbox. If you need to send 300 emails per day, that is 15 to 20 inboxes across 5 to 7 domains. Not 10 inboxes sending 30 per day each. The per-inbox limit is a hard constraint, not a starting point to negotiate upward.

List Quality: Before Any Email Goes Out

Verify every contact before sending. Unverified lists from Apollo, LinkedIn scrapers, or any other data source contain 4 to 8% invalid addresses. Run every list through an email verifier before it touches your sequences. ZeroBounce and Reoon are both reliable options. The DNS checker verifies domains in bulk if you want to do a quick domain-level pass before paying for full verification.

No links in your first email. Links trigger spam filter signals, particularly in cold emails going to addresses with no prior relationship. Your first email is plain text, one question or CTA, no tracking pixels, no links. If you want to share a resource, put it in the follow-up after someone replies.

Check your sending domains against blacklists before launch. Use the blacklist checker to confirm your domains are clean before your first campaign. A domain on a major blacklist has near-zero inbox placement regardless of how good your DNS setup is. Clean domains before you start. Check again monthly during active campaigns.

Bottom line: Do the setup right and deliverability mostly takes care of itself. Skip a step and you spend weeks troubleshooting spam placement problems that could have been avoided. Separate domains, correct SPF and DKIM and DMARC, 14-plus days of warmup, 15 to 20 sends per inbox per day, verified lists, and no links in email one. That is the full checklist. Puzzle Inbox handles the infrastructure layer. You handle the setup. Everything else follows from getting these fundamentals right.

Ready to start sending?

Puzzle Inbox provisions pre-warmed Google Workspace and Outlook 365 cold email inboxes ready to send within 24-72 hours. See the pricing page, the how-it-works walkthrough, or the our-process page for full details. Comparisons follow our editorial methodology.