How do you stop cold emails going to spam?

To stop cold emails going to spam, fix the technical basics first: send from a separate domain with SPF, DKIM and DMARC set up, warm up each inbox, and keep daily volume per inbox low. Then protect your reputation with clean, verified lists, plain and relevant emails, and an easy way to opt out. Spam filters mostly judge two things: whether you are who you say you are, and whether recipients want your email.

Why cold emails land in spam

Mailbox providers such as Gmail and Yahoo decide where an email goes based on signals they collect about the sender. The main ones are:

• Authentication: can the receiving server confirm the email really came from your domain?
• Reputation: how have recipients reacted to your past emails? Spam complaints, bounces and ignored emails all count against you.
• Volume patterns: a brand-new inbox that suddenly sends hundreds of emails looks like a spammer.
• Content: heavy links, images, tracking and pushy wording add risk, especially from a new domain.

You cannot control the filter, but you can control every one of these inputs.

Step 1: authenticate your sending domain

Google's email sender guidelines require every sender to set up SPF or DKIM, use TLS and have valid forward and reverse DNS. Senders of more than 5,000 messages a day to Gmail must set up SPF, DKIM and DMARC, with the From domain aligned. Yahoo publishes similar sender best practices.

For cold email, set all three up even if you send far less than 5,000 a day:

1. SPF: a DNS record listing the servers allowed to send for your domain.
2. DKIM: a cryptographic signature added to each email. Your email provider (Google Workspace, Zoho and so on) gives you the record to publish.
3. DMARC: a policy that tells receivers what to do if SPF or DKIM fails. Starting with `p=none` while you monitor is allowed under Google's rules.

Many teams send cold email from a secondary domain (for example `getyourbrand.com` instead of `yourbrand.com`) so that any reputation damage does not affect the main company inbox.

Step 2: warm up new inboxes and keep volume low

A new inbox has no history. Warm-up builds a track record gradually by sending small numbers of emails that get opened and replied to, increasing slowly over a few weeks.

Then cap your sending. A common, cautious approach is a modest number of cold emails per inbox per day, spread across several inboxes rather than one inbox sending everything. We cover the numbers in more detail in how many cold emails you can safely send per inbox per day.

Also add natural gaps between sends and only send within working hours in the recipient's time zone. Bursts of identical emails sent seconds apart look automated.

Step 3: clean your list before you send

Bounces are one of the fastest ways to damage a sender's reputation. Before any campaign:

• Verify every address and remove invalid ones.
• Remove duplicates, role addresses you have no reason to email, and anyone who has opted out before.
• Keep a permanent suppression list of people who unsubscribed or asked not to be contacted.

Google asks bulk senders to keep the spam rate reported in Postmaster Tools below 0.3%, and recommends staying under 0.1%. The best way to stay well under that is to email only people your offer is genuinely relevant to.

Step 4: write emails people do not report

Filters learn from recipients. If people mark you as spam, future emails go to spam. Emails that get replies help.

• Keep it short and plain. A few sentences, plain text, no attachments, one link at most (or none in the first email).
• Make it relevant. A specific, true first line about their business beats a generic compliment. See how to write a personalised first line.
• Vary your wording. Sending thousands of word-for-word identical emails is a pattern filters notice. Light variation (spintax or a few A/B versions) helps, as long as every version reads naturally.
• Avoid hype. All-caps subject lines, promises you cannot back up and fake "Re:" subjects erode trust and break consumer-protection rules in many places.
• Stop on reply. Never send a follow-up to someone who has already answered.

Step 5: stay on the right side of the law

Deliverability and compliance overlap. In the UK, the ICO's business-to-business marketing guidance says you can email corporate subscribers without prior consent, but you must not hide who you are and must give a valid way to opt out. Sole traders and some partnerships are treated as individuals, which needs consent or the soft opt-in. In the US, the FTC's CAN-SPAM compliance guide requires honest headers and subject lines, your physical address and a working opt-out honoured within 10 business days. This is general information, not legal advice.

Step 6: watch the numbers and react quickly

Check your results every week, not just at the end of a campaign:

• Bounce rate rising: pause and re-verify the list.
• Replies dropping suddenly on one inbox: that inbox may be landing in spam. Reduce its volume and let warm-up run.
• Spam complaints: tighten your targeting. Complaints mean the email reached the wrong person or the wrong message.

Set up Google Postmaster Tools for your sending domain to see the spam rate Gmail records.

A worked example

A small agency wants to send 300 cold emails a day. Instead of one inbox, it buys two secondary domains, creates three inboxes on each, publishes SPF, DKIM and DMARC for both, and warms all six inboxes for a few weeks. Each inbox then sends about 50 emails a day, in working hours, with gaps between sends. The list is verified first, each email is three or four plain sentences with a specific first line, and replies stop the sequence. If one inbox's replies drop, it is rested while the others carry the load.

Key takeaways

• Authenticate every sending domain with SPF, DKIM and DMARC.
• Warm up new inboxes and keep per-inbox daily volume low.
• Verify lists and suppress opt-outs before every send.
• Short, relevant, plain emails earn replies, and replies protect reputation.
• Follow the ICO and CAN-SPAM rules: identify yourself and make opting out easy.

FAQ

Does using a separate domain for cold email help?

It protects your main domain. If the cold email domain's reputation drops, your everyday company email is not affected. The new domain still needs authentication and warm-up.

Is warm-up enough on its own?

No. Warm-up builds early history, but reputation then depends on how real recipients react. Poor targeting will undo warm-up quickly.

Do links and images send cold emails to spam?

They do not automatically, but they add risk, especially from a new domain. Many senders leave links out of the first email and add them only after a reply.

What spam rate should I aim for?

Google says to keep it below 0.3% in Postmaster Tools and recommends under 0.1%.

If you want this set-up handled in one place, Asendify Outbound connects unlimited inboxes, runs built-in warm-up, rotates sends with daily limits, checks emails before sending and handles bounces and unsubscribes automatically; it does not set up your DNS records for you, so publish SPF, DKIM and DMARC with your email provider first.

More playbooks on other topics: https://www.asendify.co/books/

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