A new domain has zero reputation. Send 500 cold emails on day one and Gmail will park them in spam — possibly for life. Here's the 28-day schedule we use to take a fresh domain to production-ready, plus the metrics to watch.
What "warmup" actually means: slowly increasing send volume from a new IP/domain while maintaining high engagement signals (opens, replies, no spam-marks). Mailbox providers treat new senders as suspicious by default; warmup builds the reputation that earns inbox placement.
Before you start: pre-flight checks
Don't skip these. Three out of four "warmup failures" we audit are actually authentication failures.
- SPF, DKIM, DMARC records published and validating ✓
- MX records pointing to your real provider ✓
- PTR (reverse DNS) set on your sending IP ✓
- List-Unsubscribe and List-Unsubscribe-Post headers on every send ✓
- A real homepage at the sending domain (not a parked page) ✓
The 28-day schedule
Week 1 — Foundation (days 1–7)
Goal: prove you're a real sender. Volume stays tiny. Open rates should be >80% because you're only emailing real people who know you.
Day 1: 20 sends (engaged contacts only, personalized)
Day 2: 25 sends
Day 3: 35 sends
Day 4: 45 sends
Day 5: 60 sends
Day 6: 75 sends
Day 7: 90 sendsContent rule: 1:1 plain-text only. No images, no tracking pixels, no links to landing pages. Replies are gold — ask one question per email and you'll get them.
Week 2 — Ramp (days 8–14)
Goal: introduce volume signals. Start mixing in cold contacts (max 30% of daily volume).
Day 8: 120 sends (75% warm, 25% cold)
Day 10: 200 sends
Day 12: 320 sends
Day 14: 480 sendsWeek 3 — Production-edge (days 15–21)
Goal: prove sustained volume without complaint spikes. Now you can switch to your real cold-outreach copy.
Day 15: 600 sends
Day 18: 1,000 sends
Day 21: 1,600 sendsWeek 4 — Stable production (days 22–28)
Goal: lock in. Daily volume should now be within 15% of your planned production volume.
Stop the ramp if you see: spam complaint rate >0.15%, bounce rate >3%, open rate dropping >20% week-over-week, or any single-day spam-folder placement (use seedlists). Recovery is faster than rebuilding from a burned domain.
What to do during warmup
Reply to your own warmup mail
Have 5–10 friendly recipients reply to your emails. A reply is the single highest-value engagement signal to Gmail/Outlook. Two-way conversation > one-way blast.
Randomize send times
Don't send 100 emails at exactly 9:00 AM. Sparrow's send-time jitter spreads them across 9:00–11:30 AM with random 8–47 second gaps. Looks human, scores human.
Vary subject lines and bodies
Identical messages to thousands of recipients trigger bulk-mail filters. Use 4–6 subject variants and 2–3 body variants per campaign. Sparrow's spintax ({Hey|Hi|Hello}) handles this automatically.
Auto-warmup vs manual
Sparrow's auto-warmup pool exchanges emails with thousands of other warming domains. It runs in the background, builds your reputation 3–4x faster than manual, and stops automatically when you hit production volume.
| Approach | Time to 1K/day | Hands-on | Risk |
|---|---|---|---|
| Manual | 28–35 days | 1–2 hrs/day | High (easy to over-send) |
| Auto-warmup | 10–14 days | ~10 min/week | Low (pace controlled) |
Common warmup mistakes
- Skipping week 1 because "it feels slow." The single biggest cause of warmup failure. The first 7 days are when reputation is built; rushing them destroys what you're trying to create.
- Using a list with bounce risk. Always validate before sending in week 2+.
- Mixing transactional + cold from same domain. If you must, use a subdomain split:
send.brand.comfor cold,app.brand.comfor transactional. - Ignoring reply tracking. Replies are the most powerful signal. Track them, optimize for them.