Cold email deliverability checklist

Deliverability is whether your email reaches the inbox instead of spam. It rests on three things: authentication (SPF, DKIM and DMARC set up correctly), reputation (low bounces and spam complaints, built up gradually) and a clean, relevant list and message. Work through the checklist below before you send, and monitor spam rates after.

Part of our complete guide to B2B lead generation.

By the FUNEL team · Last reviewed October 28, 2026

Mailbox providers change their rules. The Gmail requirements below come from Google's published sender guidelines, reviewed on the date above. Check them again before a large campaign.

The three pillars of deliverability

  • Authentication: proof that you are allowed to send from your domain.
  • Reputation: how mailbox providers judge your sending history, based on bounces, spam complaints and engagement.
  • Content and list: who you send to and what you send.

Checklist 1: authenticate your sending domain

Example records for a fictional domain, to show the shape (your provider gives you the exact values): SPF "v=spf1 include:_spf.mailprovider.example ~all" and DMARC "v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.example".

  • SPF: a DNS record listing the servers allowed to send for your domain.
  • DKIM: a signature added to each message. Gmail requires a DKIM key of 1024 bits or longer for personal Gmail accounts and recommends 2048 bits if your provider supports it.
  • DMARC: a policy that says what to do when SPF or DKIM fails, and where to send reports. Senders of more than 5,000 messages a day to Gmail must set up SPF, DKIM and DMARC, and the policy can start at "none".
  • Valid reverse DNS (PTR) records and TLS: your email provider normally handles these.
  • Alignment: the domain in your From address should match the domain that passes SPF or DKIM.

Checklist 2: protect your main domain

Many teams send cold outreach from a separate but similar domain so that a reputation problem does not affect the main company domain used for customer email. If you do, set up authentication on it exactly as above and make sure it points to your real website.

Checklist 3: warm up new mailboxes slowly

A brand-new mailbox has no history, and a sudden burst of cold email looks like spam. Start with a small number of sends a day, mostly to people likely to reply, and increase gradually over weeks while you watch bounces and replies. Check your provider's daily limits and do not exceed them.

Checklist 4: clean the list

  • Verify every address before you send and remove invalid ones.
  • Treat catch-all, role and unknown addresses as risky and send in small batches.
  • Remove hard bounces immediately and never email them again.
  • Keep a suppression list of people who opted out.

Deep dive: How to verify emails and reduce bounces

Checklist 5: write like a person

  • Short and plain, with one reason for writing and one question.
  • Personalised to the person's role, not just a name swap.
  • At most one link, and no tracking-heavy or image-heavy layouts.
  • No misleading subject lines.
  • An easy way to opt out. For marketing and subscribed messages to Gmail from bulk senders, one-click unsubscribe is required, and it is good practice for everyone.

Checklist 6: watch the numbers

  • Spam rate: Google says to keep it below 0.3% and recommends staying below 0.10%. You can see it in Google Postmaster Tools if you send enough volume.
  • Bounce rate: keep it low and stay well under the limits your email provider publishes.
  • Reply rate and positive replies: a falling reply rate can be the first sign of a placement problem.

If deliverability drops

  1. 1. Pause and reduce volume

    Stop the campaign that is struggling. Sending more makes it worse.

  2. 2. Check authentication

    Confirm SPF, DKIM and DMARC still pass and the sending domain has not changed.

  3. 3. Check the list

    Re-verify the addresses you were sending to and remove the bad ones.

  4. 4. Check the message

    Shorten it, remove extra links and make it more relevant.

  5. 5. Restart gently

    Resume at a fraction of the previous volume and rebuild.

Sending from FUNEL

FUNEL runs email campaigns from your own connected mailboxes, with multi-step sequences that stop on reply, and finds and verifies work emails before you send. Authentication of your domain stays under your control, so use this checklist on the domain you connect.

See sequences in FUNEL →

Frequently asked questions

What do SPF, DKIM and DMARC do?
SPF lists the servers allowed to send for your domain, DKIM signs each message, and DMARC tells receivers what to do when those checks fail and sends you reports.
What spam rate is too high?
Google says to keep spam rates in Postmaster Tools below 0.3% and recommends staying below 0.10%.
How long should I warm up a new mailbox?
There is no fixed number. Start small and increase gradually over several weeks while you watch bounces and replies, and stay within your provider's limits.
Should I send cold email from my main domain?
Many teams use a separate, similar domain for outreach so a reputation problem does not affect the main domain. Authenticate it fully and point it to your real website.

Sources

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