$ man how-to/cold-email-infrastructure

Everyone obsesses over email copy. The subject line. The opening hook. The CTA. None of that matters if the email lands in spam. Deliverability is the foundation. Build it right and mediocre copy still generates replies. Build it wrong and the best copy in the world goes unread. Cold email infrastructure has three layers: domains (your sending identity), authentication (proving you are legitimate), and reputation (earning trust over time). Skip any layer and your emails hit spam within weeks.

CODE

Never send cold email from your primary domain. If your company is acme.com, buy secondary domains for outbound: tryacme.com, getacme.com, acmehq.com, useacme.com. If one domain gets burned, your main domain stays clean. How many domains: start with 3-5. Each domain gets 2-3 mailboxes. That gives you 6-15 sending accounts to rotate. For every 50 emails/day you want to send, plan for one domain with 2-3 mailboxes. Domain purchasing rules: buy .com only (other TLDs have lower trust). Keep the name close to your brand (prospects should recognize it). Avoid hyphens, numbers, or random words. Register through Google Domains, Namecheap, or Cloudflare. Mailbox setup: use Google Workspace ($6/user/month) or Microsoft 365 ($6/user/month) for your sending accounts. These have the best inbox placement rates. Avoid custom SMTP or cheap email providers - major inbox providers trust Google and Microsoft senders more.

CODE

Every sending domain needs three DNS records. These prove to inbox providers that your emails are legitimate. SPF (Sender Policy Framework): tells inbox providers which servers are authorized to send email from your domain. Add a TXT record to your DNS: For Google Workspace: v=spf1 include:_spf.google.com ~all For Microsoft 365: v=spf1 include:spf.protection.outlook.com ~all DKIM (DomainKeys Identified Mail): cryptographically signs your emails so inbox providers can verify they were not modified in transit. Google Workspace and Microsoft 365 both have DKIM setup in their admin panels. Generate the key, add the CNAME or TXT records to your DNS. DMARC (Domain-based Message Authentication): tells inbox providers what to do when SPF or DKIM fails. Start with a monitoring policy: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com After 2-4 weeks of monitoring with no issues, upgrade to: v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com Eventually move to p=reject for maximum trust. This tells inbox providers to reject any email from your domain that fails authentication. Verification: use MXToolbox or mail-tester.com to verify all three records are configured correctly before sending a single email.

PATTERN

New domains have zero reputation. Inbox providers treat unknown senders as suspicious. Warmup builds your sender reputation gradually. How warmup works: your sending accounts exchange emails with other accounts in a warmup network. These emails get opened, replied to, and marked as important. This signals to Gmail, Outlook, and Yahoo that your domain sends email that people want to read. Timeline: minimum 14 days before sending any cold emails. 21-30 days is better. During warmup, your accounts should send and receive 20-40 warmup emails per day with engagement (opens, replies, clicks). Built-in warmup tools: Instantly includes warmup in every plan. Smartlead includes it. Lemlist has Lemwarm. If your cold email tool does not include warmup, use a standalone tool like Warmbox or Mailreach. Never stop warmup. Keep warmup running even after you start cold campaigns. The ongoing warmup emails maintain your sender reputation alongside your cold outreach. Most tools let you run both simultaneously. Signs warmup is working: open rates above 60% in the warmup network, zero spam folder placements, and your domain passes all authentication checks on mail-tester.com (score 9/10 or higher).

FORMULA

The rules that keep you out of spam: Volume per account: never exceed 30 cold emails per day per account. 20-25 is safer. Combined with warmup emails, each account should send 40-60 total emails daily (20-25 cold + 20-30 warmup). Ramp schedule: week 1 after warmup: 5 cold emails/day per account. Week 2: 10/day. Week 3: 15/day. Week 4: 20-25/day. Do not jump to full volume immediately. Domain rotation: distribute your daily send volume across all domains. If you send 100 cold emails/day, use 5 accounts across 3 domains. Your cold email tool handles this rotation automatically. Send timing: business hours in the prospect's timezone. Tuesday through Thursday are highest-performing days. Avoid Monday mornings and Friday afternoons. Bounce management: keep bounce rate below 3%. If a campaign exceeds 5% bounces, pause it and clean the list. High bounce rates destroy sender reputation fast. Spam complaint rate: stay below 0.1%. Gmail's hard limit is 0.3% - above that, your domain gets flagged. Monitor this in Google Postmaster Tools. Unsubscribe compliance: include an unsubscribe link in every cold email. This is legally required (CAN-SPAM, GDPR) and reduces spam complaints because annoyed recipients unsubscribe instead of reporting spam.