A 6-week IP warmup schedule for self-hosted senders

An IP without sending history looks the same to a mailbox provider as an IP that just got handed off from a takeover. There is no signal of legitimacy — not yet. Sending 50,000 messages on day one from a fresh IP looks indistinguishable from a spammer renting a virgin IP block to send before reputation systems catch up.

So Gmail, Outlook, Yahoo, Apple iCloud Mail, and the regional providers all do the same thing on first contact: they accept a small initial volume, watch how the recipients react (open / click / mark-as-spam / delete-without-reading), and only after a few days of clean engagement do they unlock larger volumes. The "few days" is the warmup window. Skip it and you do not get blocked — you get throttled and spam-foldered for weeks afterwards, which is harder to recover from than an outright reject.

There are two ramp shapes in widespread use:

• Linear — same fixed increment per day. 50 → 100 → 150 → 200 → 250 … Predictable, slow, conservative.
• Exponential — multiplies. 50 → 100 → 200 → 400 → 800 … Reaches target volume faster but is more aggressive at the tail.

AcelleMail’s built-in warmup engine (model: app/Model/WarmupStrategy.php) supports both via the constants GROWTH_STRATEGY_LINEAR and GROWTH_STRATEGY_EXPONENTIAL, plus two convenience presets: PRESET_BALANCED (linear, moderate increment) and PRESET_CAUTIOUS (linear, smaller increment with a longer ramp window). For brand-new sending domains with no historical reputation, cautious is the safer default. For an IP migration where the From-domain already has reputation on a different IP, balanced or exponential are acceptable.

The exact numbers below are a cautious linear ramp. They are deliberately conservative; the discipline matters more than the precise figures. The single rule that breaks every warmup: never double yesterday's volume on the new IP until reputation is established. Once weekly bounce + complaint rates are clean for a week at peak, the IP is "warm" and warmup terminates.

By the end of week 1 you have proven you can send and that recipients are engaging. By the end of week 2 you are at 10,000/day — an order of magnitude jump from day one. This is when bulk-sender thresholds at Gmail and Yahoo start to apply: above ~5,000 messages/day to a single mailbox provider, the DMARC alignment, one-click unsubscribe, and complaint-rate ceilings become enforced rather than advisory. If you are missing any of those preconditions, week 2 is when it shows up — not as a block but as a quiet shift to the spam folder.

The fix is to land all three preconditions before warmup starts:

• DMARC at p=quarantine; pct=100 minimum, ideally p=reject, with RUA reports flowing.
• One-click unsubscribe via the List-Unsubscribe + List-Unsubscribe-Post headers (RFC 8058). AcelleMail emits these by default.
• Complaint-rate budget — Amazon SES enforces a hard 0.1% complaint-rate ceiling. Stay below 0.05% as a working margin.

The console command app/Console/Commands/WarmupListServers.php is the cron entry point. It iterates every active sending server with a strategy attached and applies the day-of-strategy daily cap before allowing any campaign to consume the server. The cap lives in SendingServerWarmupUsage; the per-day execution log is SendingServerWarmupLog. The strategy itself supports three limit types via constants on WarmupStrategy:

• LIMIT_TYPE_PER_DAY_CAP — "today's send budget is N, no more"
• LIMIT_TYPE_TARGET_VOLUME — "ramp until N/day is sustained, then mark complete"
• LIMIT_TYPE_STOP_AFTER_DAYS — "ramp for N days, then stop"

For most operators the right combination is GROWTH_STRATEGY_LINEAR + LIMIT_TYPE_TARGET_VOLUME: ramp linearly until reaching the daily target, then disengage warmup and run normally. The strategy can be attached to any sending server — SES, Mailgun, generic SMTP, custom — independently of the underlying driver.

If you are warming up against Amazon SES (the recommended pairing per /pricing), three numbers in the SES console "Reputation metrics" panel matter during the ramp:

• Bounce rate — AWS warns at 5%, pauses at 10%. You should be far below 2%.
• Complaint rate — AWS warns at 0.1%, pauses at 0.5%. Stay under 0.05% as the working margin.
• Daily sending limit — SES auto-grows this as your sending history accumulates. If it stops growing, your warmup ramp is outpacing the auto-grant.

Each is per-account, not per-IP, so the metric is a derivative of all your sending in aggregate. If the bounce-rate number creeps up during week 2, slow down — do not push through. The provider has noticed something and the cost of investigating now is far smaller than the cost of recovering after a pause.

You can skip warmup in two situations and only two:

1. You are using SES with shared IPs (the default — SES production accounts share a managed IP pool). The pool is pre-warmed; you inherit its reputation. Warmup is not relevant unless you upgrade to SES dedicated IPs.
2. Your existing From-domain already has reputation built on a different IP, and you are migrating to the new IP. You still warm, but on an exponential preset rather than cautious linear, because the From-domain reputation carries forward.

For everyone else — new domains, dedicated IPs, fresh self-hosted Postal MTA installs — warmup is not optional. The longer treatment with day-by-day SES dashboard interpretation lives in /guide/email-deliverability §7.