Guide
Cold Email Infrastructure: The Complete Setup Guide
How to build cold email infrastructure that lands in the inbox: how many domains, users per domain, the exact DNS records, warmup timelines, and Microsoft vs Google vs self-hosted trade-offs.
Cold email lives or dies on infrastructure. The copy matters, the list matters — but if your domains, DNS and warmup are wrong, nothing else gets a chance. This guide is the setup we automate in production, written out so you can do it by hand or judge any vendor's work.
1 · Domains: buy fresh, buy enough, never your main one
Never send cold email from your primary domain — reputation damage there hurts everything. Buy separate sending domains: variations of your brand (getacme.com, acmehq.com, tryacme.com) on mainstream TLDs (.com first). Avoid cheap spam-associated TLDs, avoid hyphens and numbers.
How many? Work backwards from volume: at 2 users per domain and 8–10 emails per user per day, one domain safely carries 16–20 cold emails a day at steady state. A 1,000-a-day target therefore needs roughly 50–63 users across 25–32 domains. Fewer users per domain (1–2) is safer than 3; never more than 3.
2 · Mailboxes: Microsoft, Google, or your own servers
Microsoft 365 packs cleanly: about 25 licensed users per fresh tenant, 8 domains per batch, 3–4 users per domain. Google Workspace provisions well via domain-wide delegation. Self-hosting (your own mail hosts, real Dovecot accounts, your own DKIM keys and IPs) gives full control and the lowest per-user cost — at the price of operating it, which is exactly what our fleet automates.
Whichever you choose: fresh personas per domain (never the same three names on twenty domains — that is a filter pattern), and credentials stored somewhere encrypted and auditable, not a spreadsheet.
3 · DNS: the four records that decide everything
Every sending domain needs SPF (one merged record — two SPF records is an automatic fail), DKIM (per-provider key, 2048-bit where supported), DMARC (start at p=none with reports, tighten later), and correct MX. Custom tracking and reply subdomains keep click redirects and replies off shared reputations.
Verify with real DNS lookups after propagation, not with your registrar's dashboard — what public resolvers serve is what mailbox providers see. Records typically propagate in minutes to hours; trust green only when a public resolver returns the record.
4 · Warmup: two to three weeks, no shortcuts
Start every new mailbox at its provider's safe floor (a handful of emails a day) and ramp gradually — roughly doubling weekly toward your per-user cap. Real warmup means real conversation-shaped mail between real mailboxes, junk-rescued when it lands wrong. Any bounce spike or spam-folder signal should pause the ramp automatically.
Only after warmup completes should campaign volume take over — and even then, keep total per-mailbox volume (warmup + campaigns) inside the cap.
Questions, answered straight
How long until a new setup can send cold email?
Domains and DNS: same day (propagation permitting). Users and credentials: same day. Warmup to full volume: two to three weeks. Budget three weeks from purchase to full-speed campaigns.
How many emails per day per mailbox is safe?
8–10 cold emails per user per day is the deliverability-safe recommendation; 5–15 is the hard band. Higher numbers trade short-term volume for long-term placement.
Can this whole setup be automated?
Yes — that is literally what emailcampaign.ai does: one approval buys the domains, creates the users, writes the DNS, retains the credentials and runs the warmup, with every step audited and blockers that resume themselves.
Or approve once and skip the manual work
The platform builds this exact setup — domains, users, DNS, warmup — behind one approval.
Free to start — no card required · One approval builds the fleet