Cold email deliverability checklist for 2026

Why does deliverability matter so much now?

Because the best message in the world does nothing in the spam folder.

Gmail and Outlook both tightened their rules. Google, Email sender guidelines asks every sender to keep spam rates in Postmaster Tools below 0.3%. Senders of more than 5,000 messages a day to Gmail also need SPF, DKIM and DMARC, with the From domain aligned.

Microsoft followed. From 5 May 2025, senders of 5,000+ messages a day to Outlook.com, Hotmail and Live addresses need SPF, DKIM and a DMARC policy of at least p=none. Mail that fails goes to junk first, with full rejection to follow (Mailgun, Microsoft Outlook sender requirements 2025).

Most cold email teams send far less than 5,000 a day per domain. Set it all up anyway. The rules show what the filters look for.

1. Are your domains set up right?

• Never send cold email from your main company domain. Use two or three similar domains, such as a "get" or "try" version of your name.
• Point each sending domain to your main website.
• Give new domains time before sending. Register first, warm later.

2. Is authentication in place?

• SPF: lists which servers may send for your domain.
• DKIM: signs each email so the receiver knows it was not changed.
• DMARC: tells receivers what to do when SPF or DKIM fails. Start at p=none, then move up.
• Custom tracking domain, if you track clicks. Better still, do not track opens or clicks in first emails.

3. Are your inboxes warm and your volume low?

• Warm each new inbox for two to four weeks before real sending.
• Keep to about 20 to 30 cold emails a day per inbox. Add inboxes, not volume per inbox.
• Spread sends through the working day, in the buyer's time zone.
• Mind the working week. Friday is not a working day in Saudi Arabia, and August is quiet across much of Europe.

4. Is your list clean?

Bounces are the fastest way to hurt a domain.

Belkins, B2B cold email deliverability rates 2026 looked at 7,530,489 cold emails sent in 2025. The average bounce rate was 1.71%, and the study calls under 2% healthy. The spread by country was wide.

• Verify every address before it enters a campaign.
• Re-verify anything older than about three months. People change jobs.
• Drop catch-all and role addresses such as info@ unless you have a reason.
• Email one or two people per company, not ten.

5. Does your copy look like a person wrote it?

• Plain text. No images, no attachments in the first email.
• No links in the first email, or at most one.
• Short. Under 100 words is a good target.
• Written or finished by a person. Phrasly, AI vs human cold email reply rates 2026 found AI-written cold email flagged as spam at 7.8%, against 2.9% for human-written.
• An easy way to say no. A line like "Reply 'no' and I will not write again" costs nothing and lowers complaints.

6. Are you watching the numbers every week?

• Spam complaint rate in Google Postmaster Tools. Stay well under 0.3%.
• Bounce rate per campaign. Pause anything above 2%.
• Reply rate per inbox. A sudden drop in one inbox often means it is landing in spam.
• Seed tests to check inbox placement at Gmail and Outlook every few weeks.

7. Are you following the rules in Europe?

GDPR applies to anyone emailing people in the EU, wherever you are based.

GDPR Recital 47 says processing personal data for direct marketing "may be regarded as carried out for a legitimate interest". That is the basis most B2B cold email relies on. It needs a real business reason to contact that person, minimal data, and a clear way to opt out.

The stakes are high. Under GDPR Article 83, the top fines reach 20 million euros or 4% of worldwide annual turnover, whichever is higher.

Some countries, Germany among them, have stricter national rules on unsolicited email (see our Germany guide for the UWG rule and its sources). Check local law before a campaign into each country, and lean on LinkedIn where email is tight.

A boutique marketing consultancy in Spain ran outreach across the US, EU and LATAM and reached 90 SQLs. Each region needed its own sending rules and its own list checks.

For why reply rates fell even for clean senders, read why cold email reply rates fell.

Questions people ask