How to Set Up Cold Email Infrastructure from Scratch

Setting up cold email infrastructure is the first and most important step in outbound. If your infrastructure is wrong, every email you write goes to spam. If it is right, you can send hundreds of emails per day that consistently reach the inbox. This guide walks through every step from buying your first domain to monitoring deliverability after launch.

Step 1: Buy Your Sending Domains

Your sending domains are alternate domains that protect your primary brand domain. If your company is acme.com, you never send cold email from acme.com. You buy domains like getacme.com, acmehq.com, tryacme.com, and send from those instead. If one gets blacklisted, your primary domain and all your transactional email (password resets, invoices, team communication) stay safe.

How many domains to buy

Each domain supports 2-3 mailboxes. Each mailbox sends 30-50 emails per day. Work backwards from your daily volume target.

Domain naming conventions

• Use variations of your brand: getacme.com, acmehq.com, tryacme.com, useacme.com, hiacme.com
• Stick to .com domains. Recipients are suspicious of .io, .co, and .xyz for cold outreach.
• Avoid hyphens and numbers. They look spammy and are hard to type.
• Buy domains that a recipient would believe if they glanced at the sender address. 'getacme.com' looks legitimate. 'acme-outreach-47.com' does not.

Where to buy

Dynadot, Namecheap, and Porkbun are the most popular registrars for cold email domains. Domains cost $10-15/year each. Avoid GoDaddy -- their DNS management interface is slow and their nameservers have historically been slower to propagate. Buy all your domains at the same registrar for easier management.

Step 2: Configure DNS Records (SPF, DKIM, DMARC)

DNS records authenticate your emails. Without them, receiving mail servers treat your messages as potentially forged. All three records are required. Missing even one significantly reduces inbox placement.

SPF (Sender Policy Framework)

SPF tells receiving servers which mail servers are allowed to send email from your domain. You add a TXT record to your domain's DNS that lists your authorized senders.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to every email you send. The receiving server checks this signature against a public key stored in your DNS. If the signature matches, the email was not tampered with in transit. Google Workspace and Microsoft 365 both generate DKIM keys during setup -- you copy the provided value into a DNS TXT record.

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

DMARC tells receiving servers what to do when SPF or DKIM checks fail. Start with a monitoring-only policy (p=none) so you can see if legitimate emails are failing authentication. After 2-4 weeks of clean reports, move to p=quarantine.

Step 3: Provision Mailboxes

Each domain needs 2-3 mailboxes. These are the actual email accounts that send your campaigns. You provision them through Google Workspace or Microsoft 365.

Google Workspace vs Microsoft 365

Use Google Workspace as your primary. Microsoft inbox placement dropped below 27% in Q1 2025, meaning nearly 3 out of 4 cold emails to Microsoft/Outlook recipients land in spam. Google-to-Google delivery remains strong. If your budget allows, add a few Microsoft mailboxes for diversification, but send the majority from Google.

Mailbox naming conventions

• Use real-sounding names: james@getacme.com, sarah.chen@acmehq.com
• Match the sender name to the person who will 'own' the campaign. If your AE is James, the mailbox should be james@getacme.com.
• Add a profile photo to each Google Workspace account. Emails from accounts with profile photos have slightly better engagement.
• Create 2-3 mailboxes per domain. More than 3 per domain concentrates too much sending volume on a single domain.

Step 4: Warm Up Your Mailboxes

Warmup is the process of building sender reputation before you send any campaign emails. Warmup tools send emails between a network of mailboxes -- your mailboxes send to the network, the network replies, and both sides move emails out of spam into the inbox. This trains email providers to treat your mailbox as a legitimate sender.

How warmup works

1. 1Connect your new mailboxes to a warmup service. Most sending platforms (Instantly, SmartLead) include warmup built in.
2. 2The service starts sending 5-10 emails per day from your mailbox to other mailboxes in the warmup network.
3. 3Recipients in the network automatically open your emails, reply to them, and mark any that land in spam as 'not spam.'
4. 4Volume gradually increases over 14-21 days, from 5-10/day to 30-40/day.
5. 5After 14-21 days, your mailbox has enough positive sending history to start campaign sends alongside continued warmup.

How to verify warmup is working

• Check your warmup dashboard daily. Inbox placement rate should climb from 40-50% in week 1 to 80%+ by week 3.
• Use Google Postmaster Tools (free) to monitor your domain's reputation. It should show 'Medium' or 'High' by the end of warmup.
• Send a test email to a personal Gmail and a personal Outlook account. Both should land in the primary inbox, not spam or promotions.
• If inbox placement stalls below 70% after 2 weeks, check your DNS records. A missing or broken SPF/DKIM record is the most common cause.

Step 5: Connect to a Sending Platform

A sending platform handles campaign sequencing, A/B testing, reply detection, and deliverability tracking. You connect your warmed mailboxes to the platform, write your email sequences, and the platform sends on schedule.

For most people starting out, Instantly or SmartLead is the right choice. Both include warmup, have clean interfaces, and support mailbox rotation (automatically distributing sends across your mailboxes to avoid per-mailbox rate limits).

Step 6: Monitor Deliverability

Infrastructure is not set-and-forget. Deliverability degrades over time if you do not monitor it. Set up these checks and run them weekly.

• Google Postmaster Tools (free) -- shows your domain reputation, spam rate, and authentication results. Set this up on day 1.
• MXToolbox blacklist check -- paste your domain and sending IPs. Check weekly for Spamhaus, Barracuda, and SORBS listings.
• Your sending platform's dashboard -- monitor bounce rate (keep under 2%), spam complaint rate (keep under 0.1%), and open rate (healthy is 40-70%).
• Monthly DNS audit -- verify SPF, DKIM, and DMARC records are still correctly configured. DNS changes from other services can accidentally break your authentication.

The Microsoft Problem

Microsoft tightened spam filtering across Outlook, Hotmail, and corporate Exchange in Q1 2025. Inbox placement for cold email dropped to 26.77%. This means if your prospect uses Outlook, there is roughly a 1-in-4 chance your email reaches their inbox -- regardless of how good your infrastructure or copy is.

The practical response: accept that Microsoft delivery is unreliable and plan around it. Send primarily from Google Workspace mailboxes. Focus your efforts on prospects using Gmail or Google Workspace (you can identify this by their MX records). Track Microsoft-specific reply rates separately so you can measure whether your infrastructure changes improve delivery over time.

Common Mistakes That Destroy Deliverability

• Using your primary domain -- one spam complaint can tank deliverability for your entire company, including customer-facing transactional email.
• Skipping warmup -- new mailboxes that start blasting 50 emails/day immediately get flagged. The 14-21 day ramp is not optional.
• Too many emails per mailbox -- exceeding 50/day triggers rate-limiting and spam filters. Add more mailboxes instead of increasing per-mailbox volume.
• Not verifying emails before sending -- sending to invalid addresses generates hard bounces. More than 2-3% bounce rate damages sender reputation across all mailboxes on that domain.
• Ignoring blacklists -- domains and IPs land on blacklists without notification. If you do not check, you will not know until reply rates drop to zero.
• Sending without a clear unsubscribe mechanism -- CAN-SPAM requires it, and Google now enforces one-click unsubscribe headers for bulk senders.

Total Cost Breakdown

Setup Timeline