The cold email deliverability checklist: 20 checks before you press send

Most cold emails don't land in spam because of one big mistake. They land in spam because of five or six small ones stacking up. Run these 20 checks — across authentication, warmup, list hygiene, content and volume — before every campaign.

Why does a pre-send checklist matter?

Sender reputation is cumulative and slow to rebuild. A single bad batch — high bounces, spam complaints, broken authentication — can drag a domain's reputation down for weeks, and recovery means starting the warmup clock again. Five minutes of checks costs you nothing; a burned domain costs you a month.

Is your authentication actually passing?

This is the foundation. If these checks fail, fix them before worrying about anything else.

1. SPF passes and resolves. Your SPF record authorises every service that sends as your domain — and it must stay under the 10-lookup limit, or SPF fails outright with a permerror.
2. DKIM signs every message. Each sending service needs its own selector with a published TXT record, and the signature must validate — one misconfigured service silently breaks it, as explained in the DKIM guide.
3. DMARC is published and aligned. At minimum a p=none policy with rua reporting so you can see who's sending as you. Ideally you've already worked toward enforcement using the DMARC rollout guide.
4. Your tracking domain is custom and aligned. Click and open tracking that runs through a shared provider domain (like the sending tool's own domain) can drag down your reputation and break alignment. Use a custom tracking subdomain on your own domain.
5. Test before you send. Run your domain through the free SPF, DKIM and DMARC tools and read a test message's email headers to confirm Authentication-Results shows real passes.

Is your domain warmed up for this volume?

A fresh domain sending 500 emails on day one is the classic reputation killer. Mailbox providers trust senders that ramp up gradually.

1. New domains ramp over 2–4 weeks. Start at roughly 20–50 emails per day per inbox and increase by 20–30% every few days as engagement stays positive.
2. Warmup inboxes are active. If you use a warmup service, confirm the warmup inboxes are actually replying and marking messages as important — dead warmup pools are worse than useless, as covered in the warmup guide.
3. Keep cold outreach off your main domain. Send cold email from a separate domain or subdomain. If the outreach domain takes a reputation hit, your main business email — invoices, replies, customer mail — stays safe.
4. Volume per inbox stays modest. A commonly used ceiling is 30–50 cold emails per day per inbox. Need more volume? Add more inboxes across more domains, don't push one inbox harder.

Is your list clean?

Bounces are the loudest signal of a low-quality list. High bounce rates tell providers your mail is unwanted.

1. Verify every address before sending. Run your list through an email verification tool and remove invalid, catch-all and risky addresses. Cold lists older than a few months should be re-verified.
2. Keep bounces under 2%. If a batch bounces above ~2%, stop, re-verify the list, and fix the source — sending through a bad list once more will do more damage than pausing.
3. Scrub bounces and unsubscribes permanently. Maintain a suppression list and never re-add an address that bounced or unsubscribed. Re-sending to them is how domains get blocked.
4. Never send to purchased or scraped bulk lists. Besides being illegal in many regions without consent, these lists are full of spam traps — addresses that exist only to catch spammers. One trap hit can land your IP on a blocklist.
5. Include a working unsubscribe mechanism. Every cold email needs a clear, working way to opt out. It's legally required in most places and dramatically reduces spam complaints — a complaint hurts far more than an unsubscribe.

Does your content trigger spam filters?

Filters score content signals alongside reputation. None of these alone decides your fate, but they add up.

1. Subject lines are natural. No ALL CAPS, no strings of exclamation marks or dollar signs, no deceptive "Re:" or "Fwd:" prefixes. Write like a person, not a banner ad.
2. Links are few and reputable. One or two links to domains you control beats five links through URL shorteners — public shorteners are heavily abused and filters treat them with suspicion.
3. Images stay minimal. An all-image email with no real text looks exactly like the phishing templates filters are trained on. Use a healthy text-to-image ratio and always include a plain-text version.
4. Drop the hype language. "Guaranteed," "risk-free," "act now," "double your revenue" — spam filters weigh this phrasing, and prospects do too. Specific, concrete language outperforms hype twice over.
5. Personalise beyond the first name. Genuine personalisation — a sentence about their company, a relevant observation — drives replies, and positive engagement is the strongest inbox-placement signal there is.

Is your sending setup safe?

A good list and good content can still underperform if the sending pattern looks robotic.

1. Stagger sends across time. Hundreds of identical emails leaving in the same minute looks automated because it is. Spread sends across the day with natural spacing between them.
2. Follow-ups are spaced and limited. Two or three spaced follow-ups per prospect is standard; more starts generating "please stop emailing me" replies — the exact negative engagement that hurts reputation.
3. Watch reply sentiment, not just reply rate. A 5% reply rate means nothing if half the replies are telling you to go away. Negative replies are a reputation signal too — suppress complainers immediately.

What should you monitor after pressing send?

The checklist doesn't end at send time. In the first 24–48 hours, watch bounces, spam complaints and reply sentiment, run your domain's records through the free toolkit if anything looks off, and check that your domain hasn't landed on a public blocklist. If placement drops, reduce volume before diagnosing — sending harder into a reputation problem only deepens it.