Cold Email Deliverability in 2026: How to Set Up Domains and Inboxes Properly

You can have the best targeting and the best copy in the world. If your emails land in spam, nobody reads them.

Deliverability is the unglamorous part of cold email, and it's where a lot of campaigns quietly fail. Reply rates drop, nobody knows why, and the team blames the copy or the list when the real problem is that the emails never reached the inbox.

Mailbox providers have also tightened their rules over the last couple of years. Setups that worked a while ago can now get emails rejected outright.

This guide walks through how to set up cold email properly in 2026, step by step, in plain English.

Why deliverability matters more than ever

Gmail, Outlook and Yahoo decide whether each email lands in the inbox, the spam folder or nowhere at all. They base that decision on a few things:

• Authentication: can they confirm the email really came from you?
• Reputation: how have people reacted to emails from your domain and inboxes before?
• Behaviour: does your sending look like a person, or like a mass mailing?
• Content: does the email look like spam?

Get these right and most of your emails reach the inbox. Get them wrong and even a perfect email goes unseen.

The rules that changed

A quick summary of the recent changes from the big providers:

• Gmail and Yahoo require bulk senders to authenticate their email properly, offer easy unsubscribing for marketing mail and keep spam complaints low. Gmail advises keeping the complaint rate below 0.1% and never reaching 0.3%.
• Gmail stepped up enforcement in late 2025. Non-compliant bulk mail to personal Gmail accounts can now be rejected outright rather than just sent to spam.
• Microsoft introduced similar rules for Outlook.com, Hotmail and Live in May 2025 for senders of more than 5,000 emails a day, with non-compliant mail rejected.

Most cold email campaigns send far fewer than 5,000 emails a day per domain, but the direction is clear: authentication and low complaint rates are no longer optional. Treat these rules as the minimum for everyone.

Step 1: Use separate domains for outreach

Never send cold email from your main company domain.

If your cold emails get marked as spam, the damage hits the domain that sent them. If that's your main domain, it can affect every email your business sends, including invoices, proposals and replies to customers.

Instead, buy a few separate domains that are clearly linked to your brand. For a company called Northfield at northfield.co.uk, that might be:

• getnorthfield.co.uk
• northfieldhq.com
• trynorthfield.co.uk

A few tips:

• Keep them recognisable. Prospects should be able to tell they're connected to your brand.
• Avoid spammy-looking domains with lots of hyphens or random words.
• Redirect them to your main website, so anyone who types the domain in lands somewhere real.
• Buy a few at once, so you can spread sending across them and have spares if one runs into trouble.

Step 2: Set up proper inboxes

Use real inboxes from a mainstream provider, usually Google Workspace or Microsoft 365, rather than cheap bulk email tools.

• Two or three inboxes per domain is a common setup. It spreads the sending without putting too much on any one domain.
• Use real names for each inbox, such as sarah@getnorthfield.co.uk, not sales@ or info@.
• Add a profile photo and a proper signature with the person's name, job title, company and main website. Inboxes with random names and stock photos look like scams, and prospects notice.
• Keep the sender consistent. If Sarah sends the first email, Sarah should send the follow-ups.

Step 3: Set up SPF, DKIM and DMARC

These three records prove to mailbox providers that your email is genuine. They're set up in your domain's DNS settings, and your email provider will give you the exact values.

SPF (Sender Policy Framework) lists which servers are allowed to send email for your domain. Without it, anyone could pretend to be you.

DKIM (DomainKeys Identified Mail) adds a digital signature to each email, so the receiving server can check it hasn't been tampered with.

DMARC tells receiving servers what to do if an email fails SPF or DKIM checks, and sends you reports. Start with a policy of "none" while you check everything is working, then tighten it over time.

All three should be in place on every sending domain before you send a single email. You can check them with free online tools that test your domain's DNS records.

Step 4: Warm up new inboxes

New inboxes have no reputation. If a brand new inbox suddenly sends 100 cold emails a day, providers see it as suspicious.

Warming up means building that reputation gradually:

• Start small, with a handful of emails a day.
• Increase slowly over two to four weeks.
• Use a warm-up tool, which sends emails between real inboxes and marks them as important, so your inbox builds a positive history.
• Keep warm-up running in the background even once you start campaigns.

It's tempting to skip this and start sending straight away. Don't. A few weeks of warm-up protects months of sending.

Step 5: Keep daily volume low per inbox

Sending lots of emails from one inbox is one of the fastest ways to damage its reputation.

A widely used guideline is to keep each inbox to a few dozen cold emails a day, including follow-ups. If you need more volume, add more inboxes and domains rather than pushing each one harder.

Also:

• Spread sending through the working day, rather than sending everything at 9am.
• Vary the timing slightly, so the pattern looks natural.
• Avoid sudden jumps in volume.

Step 6: Clean your list before sending

Bounced emails tell providers you're sending to people you don't know, which hurts your reputation fast.

• Verify every email address before it goes into a campaign.
• Remove catch-all and risky addresses, or send to them separately in small numbers.
• Keep your bounce rate low. Many senders aim to stay under 2%.
• Keep a suppression list of anyone who's unsubscribed, bounced or asked not to be contacted, and check every new list against it.

Step 7: Write emails that look like emails

Spam filters look at content too. The safest cold emails look like normal one-to-one emails:

• Plain text, no heavy formatting, images or designs.
• No links in the first email, or at most one.
• No attachments.
• Short. A few sentences, not a newsletter.
• Avoid spammy phrases like "100% free", "act now" or lots of capitals and exclamation marks.
• Personalise meaningfully. Emails that are identical apart from the first name look automated. A real reason for writing, such as a buying signal, helps both deliverability and replies.
• Consider turning off open tracking. Tracking pixels can count against you, and open rates aren't reliable anyway. Track replies instead.

Our guide to signal-led cold emails covers how to write emails that get replies.

Step 8: Make it easy to opt out

Always give people an easy way to stop hearing from you. A simple line such as "If this isn't relevant, just let me know and I won't get in touch again" works well in cold email.

When someone opts out, remove them straight away and add them to your suppression list. It's good practice, it's required under UK rules, and people who can't find a way out are more likely to click "report spam", which does far more damage.

Step 9: Monitor and act quickly

Deliverability isn't set up once and forgotten. Keep an eye on:

• Reply rates. A sudden drop often means emails have started landing in spam.
• Bounce rates. A rise usually means a data problem.
• Spam complaints. Google Postmaster Tools shows how your domain is doing with Gmail.
• Inbox placement. Placement testing tools show where your emails are landing across providers.

What to do if deliverability drops

1. Pause the affected inboxes. Don't keep sending into a problem.
2. Check your DNS records. Make sure SPF, DKIM and DMARC are still set up correctly.
3. Check your list. A batch of bad data is a common cause.
4. Review your copy. Remove links, tracking and anything that looks promotional.
5. Rest and re-warm. Let warm-up run for a week or two before sending again.
6. Rotate in fresh inboxes if needed, while the affected ones recover.

A note for agencies

If you run outreach for clients, give each client their own domains and inboxes. Shared sending infrastructure means one client's poor list or aggressive campaign can damage deliverability for everyone else. Separate setups also mean the client owns their infrastructure, which is fairer and makes them less dependent on you.

The UK rules

Cold email to businesses in the UK is covered by PECR and UK GDPR. In short, you can usually email limited companies and LLPs without prior consent, but you must say who you are, give a way to opt out and have a lawful basis for using a person's data. Sole traders and some partnerships have stronger protections. Our guide to signal-led cold emails has a short summary, and the ICO's guidance has the full rules.

Deliverability checklist

• Separate sending domains, recognisable and redirecting to your main site
• Two or three real inboxes per domain, with real names, photos and signatures
• SPF, DKIM and DMARC set up on every domain
• Inboxes warmed up for two to four weeks before campaigns
• Low daily volume per inbox, spread through the day
• Every email address verified, with a suppression list in place
• Plain text emails, no attachments, minimal links
• A clear, easy way to opt out
• Reply rates, bounces and complaints monitored weekly

Want this handled for you?

Setting up and maintaining sending infrastructure takes time, and mistakes are costly. Our Managed Growth service sets up separate domains and inboxes for every client, handles warm-up and monitoring, and runs signal-led outreach with a target of 20 qualified sales meetings in 90 days.

If you're running your own outreach, Go7 Radar finds the buying signals and press opportunities worth acting on every morning, with suggested messages, so you send fewer, better emails.

Not sure where to start? Get a free Growth Report.

FAQs

What is cold email deliverability? It's how many of your cold emails actually reach the recipient's inbox, rather than the spam folder or being rejected.

Should I send cold email from my main domain? No. Use separate domains for outreach, so any problems don't affect your main business email.

How many cold emails can I send per day per inbox? A widely used guideline is a few dozen a day per inbox, including follow-ups. For more volume, add inboxes and domains rather than sending more from each one.

How long should I warm up a new inbox? Usually two to four weeks before starting campaigns, and keep warm-up running in the background afterwards.

What are SPF, DKIM and DMARC? They're DNS records that prove your emails are genuine. SPF lists who can send for your domain, DKIM signs each email, and DMARC tells providers what to do if checks fail. You need all three.

Why are my cold emails going to spam? Common causes are missing authentication, new inboxes that weren't warmed up, sending too much from one inbox, bad data causing bounces, spammy content, links or tracking, and spam complaints.

Do the Gmail and Outlook bulk sender rules apply to cold email? The strictest rules apply to senders of more than 5,000 emails a day, but the basics, including authentication, easy opt-out and low complaint rates, are good practice for everyone and increasingly enforced.