Cold email is one of the highest-ROI outbound channels in B2B sales. A single well-crafted campaign can book 20+ qualified calls in a month. But none of that works if your emails land in spam.

The difference between a campaign that books calls and one that burns your domain comes down to infrastructure. Here's the complete setup guide we use at Advazon for every new client.

Phase 1: Domain Setup

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Use Secondary Sending Domains

Never send cold emails from your primary company domain. If that domain gets blacklisted, your website traffic, customer emails, and brand reputation take the hit.

Instead, register secondary sending domains. If your company is acmecorp.com, register domains like:

  • acmecorpteam.com
  • getacmecorp.com
  • acmecorp.io
  • tryacmecorp.com

Register 2–4 domains for a mid-scale campaign (500–1,000 emails/day). Each domain supports 2–3 inboxes, and each inbox sends 30–50 emails/day max.

We recommend Google Workspace or Microsoft 365 for inbox hosting. Both have strong sender reputations baked in.

Phase 2: DNS Authentication Records

SPF (Sender Policy Framework)

SPF tells receiving mail servers which IP addresses or mail servers are authorized to send email on behalf of your domain.

For Google Workspace:

v=spf1 include:_spf.google.com ~all

For Microsoft 365:

v=spf1 include:spf.protection.outlook.com ~all

Add this as a TXT record in your DNS. Use ~all (soft fail) rather than -all (hard fail) to start — you can tighten it later once everything is verified.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to every email you send. Receiving servers use your public key (stored in DNS) to verify the email wasn't tampered with in transit.

Setup varies by mail provider:

  • Google Workspace: Admin Console → Apps → Google Workspace → Gmail → Authenticate email → Generate new record → Add the TXT record to DNS
  • Microsoft 365: Security Portal → Email & Collaboration → Policies → DomainKeys Identified Mail (DKIM) → Enable for your domain

Use a 2048-bit key length when given the option. It's more secure and some spam filters actually score this positively.

DMARC (Domain-based Message Authentication)

DMARC ties SPF and DKIM together and tells receiving servers what to do when one of them fails.

Start with a monitoring-only policy:

v=DMARC1; p=none; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=1

After 2–4 weeks of monitoring reports (which land in your dmarc@ inbox), tighten to:

v=DMARC1; p=quarantine; pct=100; rua=mailto:[email protected]

Eventually move to p=reject once you're confident all legitimate sending is covered by SPF and DKIM.

Verify Everything

After setting up all three records, verify with these free tools:

Target: 10/10 on Mail-Tester. Anything below 8/10 means something is misconfigured.

Phase 3: Inbox Warmup

A brand new inbox has zero sender reputation. Inbox providers don't know if you're a legitimate business or a spammer — so they treat you with suspicion.

Warmup gradually builds your reputation by simulating normal email activity: sending, receiving, replying, and opening emails with a network of other inboxes.

Warmup Schedule (per inbox)

  • Days 1–7: 5–10 warmup emails/day, 100% reply rate from warmup network
  • Days 8–14: 15–25 warmup emails/day
  • Days 15–21: 30–40 warmup emails/day
  • Day 22+: Begin real outreach at 30–40 emails/day, scale slowly

We use Smartlead's built-in warmup for all Advazon client campaigns. It connects to a network of 10,000+ inboxes and automates the entire process. Instantly.ai also has a solid warmup network.

Warmup Best Practices

  • Keep warmup running in parallel with live campaigns — don't stop warmup just because you started sending
  • Never turn off warmup during an active campaign
  • Monitor your warmup inbox placement score — aim for 90%+ landing in primary inbox

Phase 4: Inbox Rotation and Sending Limits

Even a fully warmed inbox has limits. Sending too many emails from a single inbox triggers spam filters.

Our sending limits per inbox:

  • Maximum: 40–50 emails/day per inbox
  • Safe zone: 30–35 emails/day per inbox
  • With inbox rotation: Spread 300 emails/day across 8–10 inboxes

Inbox rotation means your campaign software automatically rotates sending across multiple inboxes, preventing any single inbox from hitting volume thresholds. Both Smartlead and Instantly support this natively.

Complete Infrastructure Checklist

Before launching any cold email campaign, confirm all of the following:

  1. ☐ Secondary sending domain(s) registered
  2. ☐ Google Workspace or Microsoft 365 inboxes created
  3. ☐ SPF record added and verified in DNS
  4. ☐ DKIM enabled and verified (2048-bit key)
  5. ☐ DMARC record added (start with p=none)
  6. ☐ Mail-Tester score: 10/10
  7. ☐ Inbox warmup running for minimum 3 weeks
  8. ☐ Inbox placement score: 90%+
  9. ☐ Lead list validated with ZeroBounce (<2% bounce rate)
  10. ☐ Inbox rotation configured in Smartlead or Instantly
  11. ☐ Google Postmaster Tools set up for domain monitoring

How Long Does This Take to Set Up?

Done correctly, the technical setup (domains, DNS records, inboxes) takes about 2–3 hours. Then you need 3 weeks minimum for warmup before you can safely scale sending.

At Advazon, we do the full infrastructure setup for clients in the first week of engagement — so by week 3–4, campaigns are live and booking calls. If you're trying to do this yourself, budget a full day for setup and don't rush the warmup.

Need help setting up your cold email infrastructure? Book a free audit with Advazon — we'll review your current setup, identify gaps, and give you a clear action plan.