A new sending IP has no reputation. Receivers treat it like a stranger at the door: a few polite messages are fine; a truckload on day one looks like a raid. Warmup is how you turn "unknown" into "trusted" without a spam-folder collapse that takes months to undo.
This is the schedule we use, plus the rules that matter more than the numbers.
What Warmup Actually Trains
Mailbox providers watch, per IP and per domain:
- Volume and how fast it grows
- Hard bounces and spam complaints
- Whether people open, reply, and move mail out of spam
- Whether you send on a predictable cadence
Warmup is not a ritual. It's controlled volume against your best recipients so those signals stay green while the IP is still unknown.
If you send under ~50k messages a month, a reputable ESP's shared IP is often better than a dedicated IP you have to warm yourself. Dedicated IPs pay off when you have stable, high volume and want isolation from other customers.
Before You Send Anything
- SPF, DKIM, and DMARC must pass for this stream. Don't warm a broken identity.
- Use a custom return-path / bounce domain aligned with your brand.
- Suppress hard bounces, role accounts you don't need, and anyone who complained.
- Build a "seed" list of highly engaged people (opened or clicked in the last 30 days). That list is who you mail first.
Never warm with a purchased list. That's how new IPs get listed on blacklists in week one.
A Practical Volume Ramp
Adjust the numbers to your real list size. The shape stays the same: small, engaged, then roughly double every few days if complaints stay under ~0.1% and hard bounces under ~2%.
| Day | Example volume | Who gets mail |
|---|---|---|
| 1–2 | 50–200 | Hottest openers only |
| 3–4 | 400–800 | Last 30-day engagers |
| 5–7 | 1,500–3,000 | Last 60-day engagers |
| 8–14 | Double every 2–3 days | Expand slowly toward the full list |
| 15–28 | Approach normal daily volume | Keep a consistent daily (or weekday) cadence |
If you send millions a day in steady state, the same curve applies — it just takes longer. Don't jump from 10k to 500k because "the campaign can't wait." Split the campaign across days.
Rules That Save Warmups
- Same From name, same domain, same IP. Mixing identities on a cold IP confuses filters.
- Mail when you will keep mailing. A burst then two weeks of silence resets a lot of the trust you just earned.
- Watch Gmail and Microsoft separately. One can look healthy while the other throttles. Use Postmaster Tools and SNDS from day one.
- Pause on a complaint spike. Don't "push through." Fix list quality, then resume at the last good volume.
- Don't turn on aggressive automation (win-back blasts, purchased appends) until the IP is through the first two weeks.
What "Done" Looks Like
You're through warmup when:
- You're at normal daily volume for several days
- Inbox placement on Gmail/Outlook seeds is stable
- Postmaster / SNDS reputation is not in the yellow/red
- Bounce and complaint rates look like your old IP (or better)
That's usually 2–4 weeks for modest volume, and 4–8 weeks for large dedicated IPs.
If Warmup Goes Sideways
Typical failure modes: too much volume too fast, a dirty list, missing authentication, or a domain that already had a bad reputation (the IP is new; the domain isn't). In that case, stop, clean, authenticate, and restart at a lower tier — don't keep pressing send.
Need a schedule sized to your ESP and daily volume? Send us your current numbers and we'll map the ramp.