TL;DR
Buy a new domain, set up Google Workspace or Microsoft 365, configure SPF/DKIM/DMARC, then use a warm-up tool (Instantly, Smartlead) to automatically exchange emails with a network of inboxes over 3–4 weeks before sending real cold email.
Email domain warm-up is the process of building a positive sending reputation with Gmail, Outlook, and other mail providers before you start real outbound campaigns.
Step 1: Buy the right domains. Use variations of your main domain: get-[company].com, try-[company].com, hey-[company].com. Never use your primary domain (yourcompany.com) for cold email — protect that for transactional and marketing email.
Step 2: Set up the email infrastructure. - Register a Google Workspace or Microsoft 365 account on each domain - Set up 1–2 mailboxes per domain (not more — too many mailboxes per domain looks suspicious) - Naming convention: firstname@get-company.com (not admin@ or info@)
Step 3: Configure authentication records. This is non-negotiable. - SPF (Sender Policy Framework): tells receiving servers which IPs can send from your domain - DKIM (DomainKeys Identified Mail): cryptographically signs your emails - DMARC (Domain-based Message Authentication): tells receiving servers what to do with unauthenticated mail Set all three in your DNS records. Use MXToolbox to verify they're working.
Step 4: Use a warm-up tool. Instantly.ai and Smartlead both have large warm-up networks (hundreds of thousands of real inboxes). The tool automatically sends and receives emails between your new mailbox and the network, simulating natural email activity. This builds a positive sending reputation.
Warm-up timeline: - Days 1–7: 10–20 emails/day, mostly opens and replies from the network - Days 8–14: 20–35 emails/day - Days 15–21: 35–50 emails/day - Day 22+: Ready for real outbound at 30–50 emails/day per mailbox
Signs the warm-up is working: - Warm-up open rate above 50% - Spam rate below 0.1% - No bounce notifications from the warm-up tool
After warm-up: Maintain warm-up on throughout your campaigns. Keep real email send volume below the limits. Monitor with Google Postmaster Tools (for Gmail deliverability) and the analytics in your sending platform.
From Cactus: Cactus sets up full cold email infrastructure for clients — domain purchase, DNS records, workspace setup, warm-up configuration — in a single two-hour onboarding session before any campaign work begins.
Cactus Marketing embeds with B2B tech startups to turn strategy into pipeline. We've worked with 60+ companies, supported 12 exits, and contributed to $7B+ in client valuations.
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Book a free strategy call →How do I write a cold email that gets replies?
Write one sentence that's specifically about them, one sentence on their problem, one on your solution, and one CTA. The email should be under 80 words, reference something real about their company, and ask a yes-or-no question at the end.
How do I find leads for cold email?
Start with Apollo.io or LinkedIn Sales Navigator to build a list from your ICP criteria. Enrich it through Clay or a waterfall of data providers for verified emails. Target trigger events — recent funding, new hires, job postings — to catch companies in active buying moments.
What is a good cold email reply rate?
A good cold email reply rate is 3–8% for a broad ICP campaign and 8–15% for a highly personalized, trigger-event-based campaign. Anything above 15% with meaningful volume is excellent. Below 2% means something fundamental is wrong — ICP, targeting, or the email itself.
How many cold emails should I send per day?
New domains should warm up for 2–4 weeks before sending real campaigns, starting at 10–20 emails/day and capping out at 30–50/day per domain for sustained campaigns. With multiple warmed domains running in rotation, total volume can reach 500–2,000+/day without domain damage.