Cold email is the toughest category of email to deliver. You are sending unsolicited messages to recipients who do not know you, at volume, often from new domains. Mailbox providers know this pattern intimately and treat it with extreme skepticism. The good news: cold email deliverability is a solved problem if you do the boring things right.
Step 1: Use a secondary domain
Never send cold from your primary domain. If you burn it (and you will burn one occasionally), your internal email and customer comms break with it. Buy a near-identical lookalike: acme-co.com, tryacme.com, acme.io. Set it up identically. Send cold from there.
Step 2: Warm the domain for 4 weeks before scaling
New domains have zero reputation. If you send 1,000 emails on day one, you get filtered to spam permanently. Warm up by:
- Sending 5 emails the first day, doubling every two days.
- Replying to those emails from a second inbox so engagement signals start building.
- Letting the cycle run 21 to 28 days before any real outreach.
Tools like Lemwarm and Mailwarm automate this. Use one.
Step 3: Run multiple inboxes per domain
One inbox can comfortably send 30 to 50 cold messages per day. Past that, mailbox providers see velocity and downgrade you. To scale, add inboxes on the same domain. Two to four inboxes per domain is the standard pattern.
Step 4: Verify every list before sending
This is the single biggest factor. Cold lists from Apollo, Lusha, ZoomInfo and similar tools contain anywhere from 8 to 25% invalid addresses. Sending to them spikes your bounce rate immediately, and your domain reputation is dead before the campaign finishes.
Upload every list to MailoClean bulk verifier. Send only to the valid segment. Save the risky segment for a slower nurture sequence once you have engagement.
Step 5: Authenticate properly
SPF, DKIM, DMARC. All three, passing. We have a full guide on this.
Step 6: Write like a human
Mailbox providers run content classifiers. Common cold email patterns get flagged:
- Generic openers ("I hope this email finds you well").
- Long pitches with multiple paragraphs of features.
- Multiple links in a short message.
- Tracking pixels on every email.
- HTML signatures with images.
Write three sentences, one ask, no images, one link. It is harder to write short than long. Do it anyway.
Step 7: Slow down
Spread sends throughout business hours, not in a one-minute burst. Most cold email tools have built-in send-time randomization. Turn it on. Bursts trip spam filters faster than any other behavior.
Step 8: Monitor your reputation
Set up Google Postmaster Tools for your cold domain. Check it weekly. If domain reputation drops from Medium to Low, pause sending immediately and investigate. Once it falls to Bad, recovery takes months.
Step 9: Honour unsubscribes instantly
One-click unsubscribe links are now required for senders over 5,000 messages per day. Include them. Process them in real time. People who reply asking to be removed should be removed within an hour.
The cold email checklist
- Secondary domain registered and authenticated.
- 4-week warm-up complete.
- 2 to 4 inboxes per domain, 30 to 50 emails per inbox per day max.
- Every list verified before send.
- SPF, DKIM, DMARC all passing.
- Plain-text style messages, one link.
- Send times randomized across business hours.
- Postmaster Tools monitored weekly.
- Unsubscribe one-click and instant.
FAQ
Can I send cold email from my company's main domain?
You can. You should not. The risk of damaging your primary domain reputation is not worth it.
How many cold emails per day before I am throttled?
Per inbox, 30 to 50 is the comfort zone. Above 100 daily you start tripping Gmail's velocity filters. Scale with more inboxes, not bigger volume per inbox.
Start with the foundation
The list is the foundation. If yours is dirty, nothing else matters. Run it through MailoClean before your next campaign.