What cold email deliverability actually measures
Most teams track the wrong number. Your sending tool reports a delivery rate: the percentage of emails a receiving server accepted rather than bounced. That number is almost always in the high nineties, and it tells you nothing useful, because a message routed straight to spam still counts as delivered.
What matters is inbox placement: the share of emails that land where a human will see them. The gap between the two is where cold outreach quietly dies. A campaign can show 98% delivery and 4% inbox placement at the same time, and nothing in your sequencer will tell you.
Cold email carries a structural disadvantage here. You have no prior engagement history with the recipient, no opt-in, and no established sending relationship with their mailbox provider. Every signal Gmail and Microsoft use to decide whether you are legitimate has to come from your infrastructure and your sending behaviour. That is what this checklist covers.
The cold email deliverability checklist
Work through these in order. The early items are foundational, and the later ones will not compensate for skipping them.
1. Audit the sending domain before you send anything
Plenty of teams discover they are blacklisted only after a campaign has already failed. Before the first send, establish a baseline:
- Blacklist status. Check the major blocklists (Spamhaus, SURBL, Barracuda) for both your domain and your sending IP. Being listed is recoverable, but you need to know before you spend budget on a sequence.
- DNS records. Confirm SPF, DKIM and DMARC exist and actually validate, rather than merely being present. A malformed record often fails silently.
- Domain age and history. A domain registered last week has no reputation to draw on. A domain bought second-hand may carry someone else's.
- Content signals. Run your templates against a spam words checker before they go anywhere near a live list.
If you want the whole picture in one pass rather than assembling it yourself, an email deliverability test will show placement, authentication and blocklist status together.
2. Get SPF, DKIM and DMARC right
Authentication is the price of entry. Since Google and Yahoo tightened their bulk sender requirements, missing or failing authentication is one of the few things that will get you filtered outright rather than merely scored down.
- SPF declares which servers may send on your domain's behalf. Watch the ten-lookup limit, because stacking too many
include: statements causes a permanent error that invalidates the whole record. Our SPF generator builds a valid one.
- DKIM cryptographically signs your mail so the receiving server can verify it was not altered. Use a 2048-bit key and rotate it periodically.
- DMARC tells receivers what to do when SPF or DKIM fails, and sends you reports on who is sending as you. Start at
p=none to collect data, then move to quarantine and reject once you know your legitimate senders. The DMARC generator handles the syntax.
For a deeper walk through the DNS layer, see our guide on email authentication and DNS.
3. Add BIMI once DMARC is enforcing
BIMI (Brand Indicators for Message Identification) displays your verified logo beside your message in supporting inboxes. It only works once DMARC is at quarantine or reject, which is the point: it is a visible reward for having the authentication layer in order.
Treat it as a recognition and trust signal rather than a placement fix. It will not rescue a damaged domain, but for a healthy sender it makes you identifiable in a crowded inbox and harder to impersonate.
4. Understand what warm-up can and cannot do
This is where most cold email advice goes wrong. Warm-up, meaning gradually increasing volume and often using automated send-and-reply exchanges, establishes an initial sending pattern on a new domain. That is genuinely useful, and skipping it entirely on a fresh domain is a mistake.
But warm-up is one signal among many, and it is the signal that degrades fastest once real campaigns begin. Automated warm-up traffic is engagement between mailboxes you control. It does not reflect how actual prospects treat your mail, and mailbox providers increasingly discount it. Teams routinely run warm-up for months, watch early delivery look fine, then lose placement the moment volume scales or the campaign matures, because nothing underneath ever changed.
Warm up your domain, then keep going. The factors that hold placement over time are authentication, list quality, content, sending consistency and ongoing monitoring. We covered the limits of the approach in why a warmed-up domain is not a deliverability strategy and compared the available warm-up tools.
5. Validate the list before it reaches a sequence
Bad list data damages deliverability faster than almost anything else you can do. Every hard bounce is a signal that you do not know who you are mailing, and spam traps (recycled or purpose-built addresses that exist only to catch senders using stale lists) can get you blocklisted from a single send.
- Verify every address before import, not just at purchase.
- Re-verify anything older than roughly 90 days; B2B contact data decays quickly as people change jobs.
- Watch for role addresses (
info@, sales@, support@), which draw complaints and rarely reply.
- Standard syntax-and-MX validation misses ESP-specific filters and email protection tools, which is why lists that pass basic checks still bounce.
Keeping hard bounces under 2% is the practical threshold. Above that, providers start treating your sending as careless.
6. Write templates that survive content filtering
Content filtering is no longer keyword matching. Modern filters assess structure, link reputation, image-to-text balance and how closely your message resembles bulk mail already marked as spam, and AI-generated outreach flooding inboxes has made them considerably more sensitive.
- Keep messages short and specific. Generic, templated language now reads as bulk.
- Limit links, and make sure any shortener or tracking domain you use is not itself blocklisted.
- Avoid image-only emails and heavy HTML. Plain-text-leaning messages perform better in cold outreach.
- Genuinely personalise beyond a merge field. Identical bodies at volume are a strong bulk signal.
- Include a clear, working unsubscribe path.
Our breakdown of cold email examples that damage deliverability shows the common failure patterns, and how gateway spam filters decide what gets through explains the mechanics.
7. Follow up without compounding the damage
Follow-ups are where most replies come from, and where a struggling campaign gets worse. If your first email landed in spam, the follow-up almost certainly will too, and each additional message adds volume and reinforces the pattern that put you there.
- Space follow-ups over days, not hours.
- Cap the sequence. Long chains to unresponsive contacts increase complaint risk with no upside.
- Add new context each time rather than resending the original with "just bumping this".
- Stop the sequence on reply, bounce or unsubscribe, without exception.
Before scaling follow-up volume, confirm your first message is actually reaching the inbox. Sending more into a placement problem only accelerates it.
8. Test against placement, not just opens
A/B testing subject lines against open rates is now unreliable. Apple's Mail Privacy Protection pre-loads images for a large share of recipients, inflating opens whether or not anyone read the message, so a "winning" variant may simply have reached more Apple Mail users.
Test against outcomes that survive that distortion: reply rate, meetings booked, and inbox placement measured directly through seed testing. We wrote about what sales leaders should measure instead of open rates, and our guide on Apple's Mail Privacy Protection covers the reporting impact.
9. Monitor placement continuously
Everything above is a point-in-time fix. Deliverability is not a state you reach; it is a result that decays. Provider algorithms change, domain reputation drifts, lists age, and a single bad campaign can undo months of careful sending.
The teams that hold placement treat monitoring as ongoing infrastructure: seed-list placement testing across the providers their prospects actually use, blocklist monitoring, DMARC report review, and alerting that fires when placement slips rather than when pipeline dries up. Checking once a quarter means finding out about a problem roughly a quarter too late.
What to do when deliverability drops suddenly
A sharp, unexplained drop usually traces to one of a handful of causes. Work through them in this order:
- Check blocklists first. A new listing explains an abrupt drop better than anything else and is the fastest thing to confirm.
- Look at what changed. New sending tool, new domain, a volume increase, a fresh list import, or a template change. A sudden drop almost always follows a specific event.
- Read the bounce messages. SMTP errors are more informative than they look. A 550 5.7.1 response, for example, names the policy that rejected you.
- Re-validate the list. A bought or stale list is a common trigger, particularly if bounces rose at the same time.
- Verify authentication still passes. DNS changes, domain migrations and new sending tools frequently break SPF or DKIM without anyone noticing.
- Pause before you push. Continuing to send into a placement problem deepens it. Reduce volume while you diagnose.
Where this checklist stops being enough
A checklist gets you a clean setup. It does not keep you there once you are running real volume across multiple mailboxes and domains, because the work stops being a project and becomes maintenance, the kind that has to happen every week whether or not anyone has time for it.
That is the gap the Folderly email deliverability platform is built to close: continuous placement monitoring, root-cause diagnosis when something slips, and a dedicated specialist accountable for the outcome rather than the tooling. Across 32 published Folderly case studies, the average stated deliverability is 96.7%, with a 99% median.
If you would rather start with a diagnosis of what is currently broken, our deliverability consulting team runs a full audit of your sending infrastructure.
What is inside the downloadable checklist
The free guide walks through the same territory in a printable format you can work through alongside a campaign setup:
- Start with a domain audit
- Do your domain warm-up right
- Add BIMI
- Polish your cold templates
- Don't be shy to follow up
- Use A/B testing
