Client Onboarding
IP Warming Protocol
The most important part of your setup. Done correctly, it establishes strong sender reputation. Done wrong, recovery takes months.
Why IP warming is required
New IPs have no sending history. ISPs treat unknown IPs with suspicion. Warming is the process of gradually increasing volume over 4-6 weeks, giving ISPs time to observe your patterns and build confidence in your IP.
The mechanism is engagement-driven. Gmail, Microsoft, Yahoo, and Apple all weight engagement (opens, clicks, replies, "not spam" actions) heavily in their placement decisions for unknown IPs. A new IP sending 1,000 messages with 40% open rate builds reputation fast; the same IP sending 1,000 messages to a stale segment with 5% open rate damages reputation even before volume scales. The 2025 Postmaster Tools v2 launch retired Gmail's "Domain Reputation" gauge, but the underlying signals remain: spam rate, compliance status, and the per-day delivery-error breakdown now drive the placement decision instead.
The most common mistake is sending to old, disengaged subscribers during warm-up. The first signals ISPs receive from your IP define its reputation. Send only to recent, engaged contacts in weeks 1-2.
4-Week warming schedule (single IP)
The schedule below targets a programme reaching 300K+ per IP per day at full production. The pacing is intentionally conservative early (slow doubling weeks 1-2) and faster late (full ramp in week 4). The asymmetry reflects how ISP trust accumulates: small consistent positive signals early matter more than large volume late, because once the IP earns Gmail HIGH-tier reputation, the volume tolerance opens up substantially.
| Week | Days | Max/day | Send to |
|---|---|---|---|
| 1 | 1-2 | 500-1,000 | Openers last 30 days |
| 1 | 3-7 | 2,000-7,000 | Openers last 60 days |
| 2 | 8-14 | 15,000-40,000 | Openers last 90 days |
| 3 | 15-21 | 75,000-150,000 | Engaged last 12 months |
| 4 | 22-28 | 300K - Full | Full clean list |
Gaps of 3+ days during warming reset momentum at major providers because the IP starts re-establishing predictability rather than building on existing trust. Plan around weekends: if a Saturday-Sunday gap is unavoidable, hold week 1-2 volume on Friday so Monday's send is not the first signal Gmail has seen in 60+ hours. Conservative warming with planned gaps consistently outperforms aggressive warming without them.
Monitor daily during warming
The three dashboards below populate data 24-72 hours after the first send. Check all three at the same time each day — trends matter more than single-day values, and consistent timing makes drift easier to spot. The metrics below are 2026 production thresholds calibrated to Postmaster Tools v2 (which retired the Domain Reputation gauge in September 2025).
- Google Postmaster Tools v2 — Spam rate target sub-0.10% (recommended), 0.30% hard limit. Compliance status against Bulk Sender Requirements should be "Compliant" within first week
- Microsoft SNDS — Green = good, Yellow = review, Red = stop sending. JMRP feedback loop integration recommended for complaint visibility
- Yahoo Sender Hub — Complaint rate same 0.10% threshold per Feb 2024 bulk-sender requirements; rate-limit signals (421 deferrals) visible here
- Hard bounce rate — Keep below 2% at all times; healthy clean-list ranges 0.2-0.9% (Validity 2026 benchmark)
- Spam complaint rate — Keep below 0.08%. Above 0.3% = stop immediately. Recovery takes 4-8 weeks of consistent sub-0.10%
If something goes wrong
Complaint rate above 0.3% - Stop sending immediately. Contact your account manager before resuming.
SNDS Yellow or Red - Pause Outlook/Hotmail sends. Review and suppress complainants. Contact support.
Postmaster Tools LOW reputation - Reduce to previous week volume. Do not try to push through.
Warming complete
Once you reach full production volume with stable Postmaster Tools MEDIUM/HIGH reputation and green SNDS, your warm-up is done. Your account manager will remove the daily volume caps.
Contact your account manager