A structured warmup schedule is the difference between achieving inbox delivery within two weeks versus spending months fighting spam folders. This guide provides a concrete week-by-week volume ramp-up plan with guidance on who to send to at each stage, what metrics to watch, and the rules that determine whether you progress or pause.
The Core Warmup Rules
These rules apply throughout the entire warmup period — violating any of them during warmup can set back your progress significantly:
- Never skip a stage — each volume level is a trust test. ISPs need to see sustained clean performance before trusting higher volumes.
- Send to your most engaged recipients first — every stage should start with your highest-engagement segment, then expand to less-engaged over subsequent days within the stage.
- Pause if any metric crosses its threshold — see the pause thresholds below. Do not continue increasing volume while a metric is out of range.
- Send daily during warmup — gaps of more than 2–3 days between sends slow the warmup. Consistent daily sending builds reputation faster than infrequent large sends.
- Authenticate everything — SPF, DKIM, and DMARC must all be passing before you begin. Authentication failures during warmup are an immediate red flag.
Complete Warmup Schedule
| Period | Daily Volume | Segment to Send To | Pass Criteria to Advance |
|---|---|---|---|
| Day 1–2 | 50 | Your own team + seed list (people you know personally will open) | Open rate >60%; zero hard bounces; zero complaints |
| Day 3–5 | 100 | Most engaged subscribers — interacted in last 7 days | Open rate >50%; bounce <0.5%; zero complaints |
| Day 6–8 | 250 | Highly engaged — opened or clicked in last 14 days | Open rate >40%; bounce <1%; complaint <0.05% |
| Day 9–11 | 500 | Engaged — opened in last 30 days | Open rate >35%; bounce <1.5%; complaint <0.08% |
| Day 12–14 | 1,000 | Active subscribers — any engagement in last 60 days | Delivery rate >95%; bounce <2%; complaint <0.1% |
| Week 3 | 2,000 | Broader active list — any engagement in last 90 days | Delivery rate >96%; bounce <2%; complaint <0.1% |
| Week 4 | 5,000 | Full list minus dormant (>90 days no engagement) | Delivery rate >97%; bounce <2%; complaint <0.1% |
| Month 2 | Up to plan daily limit | Full list including dormant re-engagement campaign | Maintain all production metrics |
Pause Thresholds — When to Stop and Investigate
If any of these thresholds are crossed at any stage, pause your warmup immediately and do not increase volume until the issue is resolved:
| Metric | Pause If | Investigation Action |
|---|---|---|
| Hard bounce rate | > 2% on any single send | Export and remove all hard bounces from list; validate remaining addresses |
| Spam complaint rate | > 0.1% | Review consent practices; audit the sending segment; check whether recipients expected the email |
| Delivery rate | < 92% overall | Check domain and IP blacklist status; verify authentication; check Google Postmaster Tools |
| Open rate | < 15% in weeks 1–2 | Emails may be in spam — perform inbox placement test; review subject line and sender name |
| Google domain reputation | Drops to "Low" in Postmaster Tools | Stop volume increase immediately; investigate complaint and bounce sources; send only to very high-engagement segment until reputation recovers |
Warmup for Different Sending Scenarios
Scenario A — Brand New Business, Brand New List
Build your list organically through sign-ups as you warm up. If your list is small (under 1,000), the warmup takes less time since you naturally cannot exceed the volume targets anyway. Follow the schedule above, treating each new opt-in as part of your engaged segment.
Scenario B — Migrating from Another ESP
Even with an established sender reputation on your old provider, you must warmup on MigoSMTP because:
- Your previous ESP's IP reputation does not transfer — it belonged to their IPs.
- Your domain reputation does transfer — a well-established domain with a clean history shortens warmup from 6–8 weeks to 3–4 weeks.
Migration warmup tip: start with the same transactional emails that your old ESP was successfully delivering. These have the highest expected open rates and demonstrate clean sending immediately.
Scenario C — Returning After a Long Gap
If your domain has not sent email in more than 6 months, treat it like a new sender and follow the full schedule from Day 1. Lists that have been inactive lose quality fast — run a re-engagement campaign on your old provider first if still possible, then migrate only the active responders to MigoSMTP for the initial warmup sends.
Adjusting the Schedule for Your List Size
If your total list is smaller than the Day 12–14 target of 1,000, simply compress the schedule — spend 2–3 days at each stage rather than progressing by day count. The key is clean metrics at each level, not hitting the calendar targets.