How to warm up a new email domain — 30-day guide
A domain registered today has no sending history. ISPs cannot distinguish it from a spam operation that registered this morning. Email warmup solves this by building a controlled history of positive engagement over 30 days — before any cold outreach campaigns run at volume. Skip it, and most of your first campaign goes to spam.
Key takeaways
- A new domain has no sending history, so warmup builds a controlled history of positive engagement over 30 days before cold outreach campaigns run at volume.
- Before starting warmup, set up SPF, DKIM and DMARC, use a separate domain for cold outreach, allow 30 days before campaign volume and check IP reputation.
- Run placement tests every 5–7 days during warmup, keep warmup running after campaigns start and slow down if placement drops despite a rising warmup score.
Why ISPs need a warmup period
Gmail, Outlook, and other major providers track the sending history of every domain and IP that delivers mail to them. When a new domain appears, there is no history — it could be a legitimate sales team or a spam operation that registered an hour ago. ISPs respond to that uncertainty with higher spam placement rates and lower delivery thresholds.
Warmup addresses this by sending low volumes of mail — initially through a seed network of real inboxes — that generates positive engagement signals (opens, moves to inbox, replies). ISPs register this history under the domain's sending record, and by day 30, the domain has enough established behavior to sustain higher volumes without triggering filters.
Four things to do before starting warmup
Warmup builds on what is already in place. Starting without these is like warming up a domain that will need to be rebuilt anyway.
SPF, DKIM, and DMARC must be set first
Warming up a domain with broken authentication is wasted effort. The reputation you build will need to be rebuilt once authentication is corrected. Set up all three records, verify them with a placement test, then start warmup.
Use a separate domain for cold outreach
Do not warm up your primary business domain for cold outreach. A separate sending domain protects your main domain's reputation. If the outreach domain gets blacklisted, your transactional and newsletter mail continues unaffected.
Allow 30 days before campaign volume
New domains need at least 30 days of warmup before they can sustain 500+ email/day campaign volumes without triggering spam filters. Pressure from pipeline rarely justifies shortening this — a blacklisted domain costs more time to recover.
Check your IP reputation, not just domain
Domain reputation and IP reputation are tracked separately. A well-warmed domain on a newly allocated or previously abused dedicated IP can still land in spam. Confirm the IP's history before sending campaigns from it.
The 30-day warmup schedule
Volume targets are indicative — adjust based on your inbox placement test results. If placement drops, slow down. If it holds steady, you can ramp slightly faster.
- Days 1–7
10–25 emails/day — Establish first sending history
No real campaigns. Warmup traffic only. ISPs note the domain exists.
- Days 8–14
25–75 emails/day — Build initial engagement signals
Maintain 95%+ positive engagement (opens, replies) from seed network.
- Days 15–21
75–200 emails/day — Establish stable reputation
You can begin low-volume real sends (50–100 contacts/day) if placement tests are green.
- Days 22–30
200–500 emails/day — Ramp toward campaign volume
Monitor inbox placement at Gmail and Outlook continuously. Slow down if placement drops.
- Days 31+
500–1,000+ emails/day — Sustain and monitor
Do not stop the warmup tool. Keep running warmup in parallel with real campaigns.
Mistakes that cause warmup to fail
Most domain warmup failures come from one of four predictable errors.
Why the seed network matters
A warmup tool's seed network is the pool of inboxes that receive and positively engage with your warmup emails. The quality of that network determines whether the engagement signals it generates are trusted by ISPs.
Most warmup tools use synthetic seed addresses — mailboxes created specifically for warmup, receiving hundreds of warmup emails per day from dozens of customers. ISPs have fingerprinted most of these networks. When they see positive engagement from seed addresses they recognise, those signals carry less weight. Your warmup score rises, but your inbox placement does not improve proportionally.
A seed network built from real customer inboxes — business mailboxes that receive normal mail alongside warmup traffic — generates engagement signals ISPs treat the same as real human interactions.
Start warming up your new domain — free
InboxPlease's real-inbox seed network builds your domain's sending history with trust signals ISPs recognise. Includes inbox placement testing and blacklist monitoring throughout the warmup period.
Start freeFounder & CEO of InboxPlease. Over a decade building email infrastructure for SaaS businesses; writes about deliverability, inbox placement and sender reputation.