How to Build Email Warm-Up Infrastructure
The foundation of every cold outbound operation. Get this wrong and nothing else matters.
Why Warm-Up Exists
Email providers (Google, Microsoft, Yahoo) assign reputation scores to sending domains. A brand-new domain has zero reputation. If you start sending 200 cold emails per day from a domain with no history, inbox providers classify you as a spammer immediately. Your emails land in junk folders. Your domain gets blacklisted. The campaign fails before it starts.
Warm-up is the process of gradually building sender reputation by sending small volumes of email that get opened, replied to, and marked as important. This signals to inbox providers that your domain sends legitimate mail. Once reputation is established, you can ramp to production volume with inbox placement rates above 90%.
Step 1: Register Sending Domains
Buy 3-5 secondary domains for outbound. Keep them close to your primary brand. If your company is acme.com, register acmeapp.com, getacme.com, acmeteam.com, or acme.io. Avoid domains that look spammy (acme-offers.com, best-acme-deals.com).
Use a mainstream registrar (Namecheap, Cloudflare, Google Domains). Avoid registrars with poor abuse handling. The domain age doesn't matter as much as you might think. A 1-week-old domain with proper warm-up outperforms a 6-month-old domain that was never warmed.
Purchase domains immediately. They need time to age slightly (72 hours minimum) before you start the warm-up process. Some practitioners wait 1-2 weeks. The waiting period is debatable, but the warm-up process itself is not.
Step 2: Configure DNS Records
Every sending domain needs four DNS records configured correctly. Missing any of these causes immediate deliverability problems.
SPF (Sender Policy Framework): A TXT record that tells inbox providers which mail servers are authorized to send email from your domain. Your email provider (Google Workspace, Microsoft 365) gives you the exact record to add. Typically something like: v=spf1 include:_spf.google.com ~all
DKIM (DomainKeys Identified Mail): A cryptographic signature that proves the email was sent by your domain and wasn't modified in transit. Your email provider generates a public key that you add as a TXT or CNAME record. This is the most frequently misconfigured record.
DMARC (Domain-based Message Authentication): A policy record that tells inbox providers what to do when SPF or DKIM checks fail. Start with a monitoring policy: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com. After warm-up, tighten to p=quarantine or p=reject.
Custom tracking domain: Your outbound sequencing tool (Instantly, Smartlead, Lemlist) uses a tracking domain for open and click tracking. Set up a CNAME record pointing to the tool's tracking server. Using the tool's default tracking domain is a spam signal because that domain is shared across thousands of senders.
Step 3: Create Mailboxes
Set up Google Workspace or Microsoft 365 mailboxes on each sending domain. Google Workspace costs $7.20/user/month. Microsoft 365 Business Basic costs $6/user/month. Either works. Google has slightly better deliverability for B2B, but the difference is marginal.
Create 2-3 mailboxes per domain: firstname@domain.com, firstname.lastname@domain.com, and a backup. Fill out the profile: add a profile photo, write a short bio, and set a signature with your name, title, company, and website link. Empty profiles are a spam signal.
Enable two-factor authentication on every mailbox. Connect each mailbox to your outbound sequencing tool. Test that you can send and receive email from each mailbox manually before starting automated warm-up.
Step 4: Run Automated Warm-Up
Connect your mailboxes to a warm-up tool. Instantly includes warm-up in its plans. Smartlead has built-in warm-up. Standalone options include Warmbox, Mailwarm, and Lemwarm. The warm-up tool sends emails between your mailboxes and a network of other mailboxes, automatically opening them, replying, and marking them as important.
Start at 5-10 warm-up emails per day per mailbox. Increase by 3-5 per day. Target 40-50 warm-up emails per day after 2-3 weeks. Monitor inbox placement rates in the warm-up tool's dashboard. You want to see 95%+ inbox placement before starting cold outreach.
Do not rush this step. Two weeks of patient warm-up saves you from months of deliverability problems. Every GTM Engineer who has burned a domain learned this lesson the expensive way.
Step 5: Ramp Cold Volume Gradually
After 2-3 weeks of warm-up with 95%+ inbox placement, start sending cold emails. Begin at 10-15 cold emails per day per mailbox. Keep warm-up running simultaneously (this is important; do not disable warm-up when you start sending cold mail).
Increase cold volume by 5-10 emails per day per week. Monitor your bounce rate (keep under 3%), spam complaint rate (keep under 0.1%), and reply rate (a healthy indicator of engaged recipients).
If bounce rates spike above 5% or inbox placement drops below 80%, reduce volume immediately. Diagnose the cause: bad data, aggressive copy, or a domain reputation hit. Fix before scaling back up.
Target steady-state: 50-75 cold emails per day per mailbox. With 3 mailboxes across 5 domains, that's 750-1,125 emails per day. Plenty for most outbound campaigns. If you need more volume, add domains and mailboxes. Don't push individual mailboxes past 75-100/day.
Step 6: Monitor and Maintain
Warm-up is not a one-time setup. It's ongoing maintenance. Check these weekly:
Inbox placement rate. Use GlockApps or mail-tester.com to test deliverability across Google, Outlook, and Yahoo. 90%+ is good. Below 80% is a problem.
Blacklist status. Check MXToolbox for blacklist inclusion. If a domain lands on a blacklist, pause sending from it immediately and request delisting.
Google Postmaster Tools. If you're sending to Gmail addresses (you are), Google Postmaster Tools shows your domain reputation, spam rate, and authentication pass rates. This is the most authoritative deliverability data available. Set it up for every sending domain.
DNS record validity. Misconfigurations happen. Registrar updates, CDN changes, or accidental edits can break SPF/DKIM/DMARC. Run a monthly check using dmarcly.com or similar tools.
Infrastructure Checklist
Quick reference for the complete setup. Run through this list before launching any cold outbound campaign.
1. 3-5 secondary sending domains registered (not your primary domain)
2. SPF, DKIM, DMARC, and custom tracking domain configured for each
3. Google Workspace or Microsoft 365 mailboxes created (2-3 per domain)
4. Profiles completed (photo, bio, signature)
5. Warm-up tool connected and running for 2+ weeks
6. Inbox placement at 95%+ before cold sends begin
7. Cold volume ramping at 5-10/day per mailbox per week
8. Monitoring dashboard configured (GlockApps, Postmaster Tools, MXToolbox)
For detailed tool comparisons of outbound sequencing platforms, check the outbound sequencing tools directory. For deliverability fundamentals, see the glossary.
Frequently Asked Questions
How long does email warm-up take?
Plan for 2-4 weeks minimum. Start by sending 5-10 emails per day and increase by 5-10 per day each week. Most warm-up tools automate this ramp. Aggressive warm-up (reaching full volume in under two weeks) risks spam classification. Patient warm-up protects your sender reputation long-term.
How many sending domains do I need?
One sending domain per 50-75 emails per day is a safe ratio. If you plan to send 300 cold emails daily, set up 4-6 sending domains. Each domain needs its own mailbox, DNS records, and warm-up cycle. More domains spread risk and improve deliverability.
Can I use my primary company domain for cold outreach?
Never use your primary domain for cold email. If the domain gets flagged or blacklisted, your entire company email (support, billing, internal) is affected. Always use a secondary sending domain. Format it similarly to your primary (getcompany.com, trycompany.com, company.io) so it looks legitimate to recipients.
Source: State of GTM Engineering Report 2026 (n=228). Salary data combines survey responses from 228 GTM Engineers across 32 countries with analysis of 3,342 job postings.