Cold Email Infrastructure

The single most important rule of cold email infrastructure is this: never send cold outreach from your primary business domain. The domain you use for company email, your website, and customer communications is irreplaceable. If it gets flagged as a spam source, it damages deliverability for every email your company sends, including to paying customers. Separate sending domains are not optional. They are the foundation of a sustainable outbound operation.

The standard setup is to buy two to four domains that are similar variations of your primary domain. If your business domain is acmecorp.com, your sending domains might be tryacmecorp.com, meetacmecorp.com, and getacmecorp.com. Register them through a reputable registrar: GoDaddy, Namecheap, and Google Domains (now Squarespace Domains) are all fine. Domain registration costs $10 to $15 per year per domain. This is among the most cost-effective investments in your entire outbound stack.

For each sending domain, you need a Google Workspace mailbox. Google Workspace Business Starter runs $6 per user per month. Each domain gets one or two inboxes. The typical ratio is one to three inboxes per domain, with each inbox sending no more than 40 to 50 emails per day once fully warmed. To reach 500 sends per day, you need approximately 10 to 12 warmed inboxes across 4 to 6 domains. Plan your domain and inbox count based on your target daily send volume.

Once you have your domains and inboxes provisioned, configure email forwarding from each sending domain back to your primary inbox. Replies and bounces that arrive at meetacmecorp.com should land in your main inbox so nothing gets missed. Most domain registrars and Google Workspace both support forwarding rules that handle this automatically.

Email authentication records are the technical proof that you are who you say you are. Without them, receiving mail servers have no way to verify that emails from your domain actually originated from you, which means they route them to spam. Getting these three records right is not optional if you want inbox placement.

SPF (Sender Policy Framework) is a DNS TXT record that specifies which mail servers are authorized to send email on behalf of your domain. For Google Workspace, the record looks like this: v=spf1 include:_spf.google.com ~all. You add this as a TXT record in your domain registrar's DNS settings. The ~all at the end means "soft fail" for unauthorized senders, which is the standard setting. One SPF record per domain: do not add multiple SPF records or they will conflict and cause authentication failures.

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to every outgoing email. The receiving server checks this signature against a public key published in your DNS to verify the message has not been tampered with in transit. In Google Workspace, you generate the DKIM key under Admin Console then Apps then Gmail then Authenticate Email. Copy the generated TXT record value and add it to your domain's DNS under the provided subdomain, typically google._domainkey.yourdomain.com. DKIM takes up to 48 hours to propagate.

DMARC (Domain-based Message Authentication, Reporting, and Conformance) sits on top of SPF and DKIM and tells receiving servers what to do with emails that fail authentication. Start with p=none, which monitors without taking action and sends you reports: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com. After 30 days of clean reports showing all legitimate email passing authentication, escalate to p=quarantine and eventually p=reject. This progression protects your domain from spoofing while you build confidence that your authentication is correctly configured.

Always verify your setup using free tools like MXToolbox, Mail-Tester.com, or the test button inside Instantly.ai before sending a single campaign email.

A brand-new email inbox has zero sending history and zero reputation. If you enroll it in a 500-email-per-day campaign on day one, every major email provider will flag it as suspicious and route those emails to spam. Email warmup is the process of gradually building your inbox's reputation over 3 to 4 weeks by exchanging genuine-looking emails with other real inboxes.

The mechanics of warmup are simple: your inbox sends a small number of emails per day to other inboxes in the warmup network, those inboxes reply to your emails and mark them as important, and the back-and-forth activity signals to Gmail, Outlook, and other providers that your inbox is a legitimate communication account. Warmup tools like Instantly.ai's built-in warmup feature, Mailwarm, and Lemwarm automate this process across a shared network of warmed inboxes.

Week 1: start at 5 to 10 warmup emails per day per inbox. No campaign sends yet. Week 2: ramp to 15 to 20 warmup emails per day. Begin sending a small number of real campaign emails, no more than 10 per inbox per day. Week 3: increase warmup to 25 to 30 per day and campaign sends to 20 to 30 per inbox per day. Week 4 and beyond: maintain 20 to 30 warmup emails per day indefinitely while scaling campaign sends to 40 to 50 per day per inbox. The warmup emails counterbalance the risk signals from your cold outreach volume.

Never turn warmup off completely once you start campaign sends. Warmup is not a one-time activity but an ongoing insurance policy for your sending reputation. Instantly.ai's warmup feature runs passively in the background once enabled, so there is no ongoing management required. The $37 per month cost for Instantly Growth covers unlimited warmup across all connected inboxes, making it the most cost-effective approach for most teams.

Instantly.ai has become the dominant cold email sending platform for good reasons: it handles inbox rotation natively, its warmup network is large and well-established, and its deliverability monitoring tools give you real-time visibility into spam placement. The interface is clean enough that most users are sending their first campaign within an hour of signing up.

Inbox rotation is the feature that makes Instantly particularly valuable for volume senders. Rather than sending all 500 daily emails from a single inbox, rotation distributes sends across all connected inboxes automatically. This keeps each individual inbox well below the safe sending threshold of 40 to 50 per day while allowing your aggregate daily volume to scale. Connect 12 warmed inboxes and you can send 480 to 600 emails per day from a rotation that no individual inbox will flag.

Campaign configuration in Instantly covers four key areas. Sending schedule: set your campaigns to send on weekdays between 8am and 5pm in your prospect's local timezone, which Instantly handles automatically through timezone detection. Daily sending limits: cap each inbox at 35 to 40 sends per day to leave a buffer below the 50-send threshold. Stopping conditions: enable automatic campaign pausing if a prospect replies or books a meeting, so you do not continue emailing someone who has already responded. Unsubscribe handling: Instantly adds a one-click unsubscribe link and automatically removes opt-outs from all future campaigns to maintain CAN-SPAM and GDPR compliance.

Monitor your campaign-level stats weekly. The key metrics in Instantly are sent count, open rate, click rate, reply rate, and bounce rate. A bounce rate above 3 percent means your list quality needs attention. An open rate below 35 percent suggests deliverability issues. Reply rate below 1 percent usually points to a messaging problem rather than an infrastructure problem. Separately checking the Deliverability tab shows you inbox placement rates by email provider, letting you catch spam folder routing before it compounds.