How the ramp-up schedule works
The formula behind each day's sending target, how a 30-minute scheduler spreads sends across the day, and how it compares to published ESP ramps.
Published August 20, 2026 · 4 min read
Every domain in WarmEnvelopes gets its daily sending target from one formula: min(start + increment × days since start, max), counted in UTC days. A scheduler then runs every 30 minutes and sends just enough to keep the day on pace, so warm-up mail trickles out across the whole day instead of firing in a burst. On the free plan the target is fixed at 4 emails per day; on Pro, all three numbers are yours to set.
The daily target: a linear ramp with a cap
Three settings define the ramp for each domain:
- start — the day-one volume. Pro range 1–50, default 4.
- increment — how much is added per day. Pro range 0–50, default 2.
- max — the ceiling the ramp levels off at. Pro range up to 1,000, default 50.
With the defaults, day 1 targets 4 emails, day 7 targets 16, day 14 targets 30, and the ramp reaches its cap of 50 on day 24, holding there until you stop it. Days are counted in UTC, so the target steps up exactly at midnight UTC rather than drifting with your timezone. The free plan locks all three settings and sends a flat 4 per day — a steady baseline rather than a ramp; the pricing page has the full plan comparison.
How sends are spread across the day
A cron tick runs every 30 minutes. Each tick computes floor(target × fraction of the day elapsed) − already sent today, looking one tick ahead so the day's full target completes by midnight instead of leaving a perpetual remainder. Two useful properties fall out of that arithmetic:
Smooth pacing. A target of 48 becomes one email every 30 minutes across the entire day; nothing ever resembles a burst. That is exactly what Google's sender guidelines ask for — "Send email at a consistent rate. Avoid sending email in bursts." — and it is a rule ESPs encode as hourly caps: Resend pairs every daily warm-up figure with an hourly maximum, and SendGrid's automated warmup is expressed only in hourly limits.
Self-healing after downtime. Because each tick derives the day's expected progress from elapsed time rather than from the previous tick, missed ticks don't shift the schedule — the next one sends the shortfall and carries on, never exceeding the daily target. That matters because consistency is a first-class reputation signal: Mailgun's 15-stage warm-up plan (updated March 2026) warns explicitly that skipped days reset progress. While a warmup is running here, no day gets skipped.
Checked against what ESPs publish
We compared nine published ramp schedules while designing this — SendGrid, Amazon SES, Litmus, Klaviyo, Braze, Postmark, Resend, Mailgun, and MailReach. Two patterns hold across all of them.
Growth slows as volume rises. SendGrid's generic warm-up table doubles daily only through day 8, while the absolute numbers are small, then decays to roughly +21–33% per day; AWS's 40-day schedule decays the same way, from about 2× daily early on to single-digit percentage growth by week five. The underlying rule: doubling from 4 to 8 is invisible to a filter, doubling from 400,000 to 800,000 is a volume anomaly.
Starting volumes are small. SendGrid's table starts at 50 per day, Postmark advises 50–100 per major provider on days one and two, and cold-outreach guidance from MailReach starts at 5–10 per day per inbox with a never-more-than-20%-per-day rule.
A linear ramp gives you the first property for free: adding a fixed increment means percentage growth falls automatically as volume rises. With the defaults, +2 per day is +50% growth on day one and under +5% by the time the domain approaches its cap. And the default starting volume sits at the conservative, low-volume end of the published range:
| Schedule (published) | Day 1 | Day 7 | Day 14 | Shape |
|---|---|---|---|---|
| SendGrid generic warm-up | 50 | 8,000 | 150,000 | ×2 daily, decaying to +21–33%/day |
| Resend, new domain | 150–400 | up to 2,000 | — | stepped, with hourly caps |
| MailReach, cold outreach | 5–10 | 15–25 | 30–50 | ≤ +20%/day |
| WarmEnvelopes defaults | 4 | 16 | 30 | +2/day linear, cap 50 |
These schedules target different senders — SendGrid's table ramps a bulk sender toward a million emails a day, while the defaults here ramp a new domain toward a modest, sustainable history. If your steady state is higher, Pro's ranges cover everything short of genuine bulk-ESP territory, and how many weeks to run the ramp depends on that target — how long to warm up an email domain works through the published evidence.
What the schedule does not decide
A pacing algorithm controls volume and timing, nothing else, so it is worth being explicit about the boundaries:
- No schedule guarantees the outcome. SendGrid attaches that caveat to its own table — results vary with list quality, engagement, and content. Laura Atkins of Word to the Wise goes further: there is no single correct warm-up formula, each sending identity warms differently, and you can only warm a domain to the reputation of the mail it actually sends.
- Content and recipients are handled separately. Each send picks a random message from the template library and delivers it to one of your own inboxes.
- You can watch it work. Every attempt is logged with sender, template, status, and any error, so the dashboard shows each day's progress against its target rather than asking you to trust the formula.
Frequently asked questions
What happens if a scheduled send is missed?
Nothing is lost. Every tick recomputes how many emails the day should have produced by now from the fraction of the day elapsed, so after any downtime the next tick sends the shortfall and the schedule is back on pace — without ever exceeding the day's target.
Can I make the ramp faster on the Pro plan?
Yes — the start can go up to 50 emails per day, the daily increment up to 50, and the cap up to 1,000. Published ESP schedules slow their growth as volume rises, though, so an aggressive increment is more defensible at low volumes than near a high cap.
Why does the free plan send exactly 4 emails per day?
The free plan holds a flat 4 emails per day per domain, with the ramp settings locked. That is enough to build the daily, consistent history a low-volume domain needs, but there is no ramp — configurable start, increment, and cap are what the Pro plan adds.