Email Warming Overview
Email Warming Overview
Purpose
New mailboxes can't send 500 emails a day on day one — they get flagged as spam. Warming gradually builds a sending reputation by starting low and increasing volume over time, establishing your mailbox as a legitimate sender. This article explains how warming works in SuperSend and what to expect from the warming dashboard.
Why Warming Matters
When you connect a fresh mailbox to a sending campaign, email providers like Google and Microsoft are watching. A new mailbox that immediately blasts hundreds of emails looks like spam activity. Warming solves this by:
- Starting with a small daily send volume (e.g., 5–10 emails/day).
- Gradually increasing volume each day over a 14-day initial warmup period.
- Running "background warming" indefinitely after the initial period — a low-volume stream of warm-up emails that keeps the mailbox's reputation active even on days when your campaigns don't send much.
The warming emails are real messages exchanged with a network of other warming mailboxes. They land in inboxes, get opened and replied to, and simulate healthy inbox activity.
The Two Warming Phases
Initial Warmup (Day 1–14)
This is the ramp phase. SuperSend limits daily sending from the mailbox and gradually increases it. The warming dashboard shows "Day 7 of 14" or similar for each mailbox in this phase. Most mailboxes complete initial warmup within two weeks.
Background Warming (After Day 14)
Once initial warmup completes, the mailbox shifts to background warming. SuperSend continues sending a low volume of warming emails daily, maintaining reputation. Background warming runs indefinitely unless you turn it off. Mailboxes in background warming show a green "Background" badge on the warming dashboard.
When a mailbox finishes initial warmup and is in a healthy state, the dashboard shows a "Ready to Go!" banner. At this point, it's safe to ramp your campaign sends.
The Warming Dashboard
Go to Warming from the left sidebar.
Stat Cards
At the top of the page, four summary cards give you a snapshot:
Card | What it shows |
|---|---|
Total Warming | Total mailboxes currently warming, broken down by Initial vs Background |
Avg Health Score | Average health score across all warming senders. Green ≥80%, yellow ≥60%, red <60% |
Inbox Rate | The percentage of warming emails landing in the inbox (vs. spam). From placement test data. Green ≥95%, yellow ≥90%, red <90% |
Need Attention | Count of senders with active problems. Click it to filter the list below to just those senders |
Status Filter Tabs
Below the stat cards, filter the sender list by:
- All — shows every mailbox currently in warming
- Initial Warmup — just the mailboxes in the 14-day ramp phase
- Background — mailboxes that have completed initial warmup and are maintaining
- Problems — mailboxes with health issues that need attention
The Warming Chart
Two views, toggled by tabs:
Initial Warmup view
A bar chart showing how many senders are on each day of the 14-day warmup. If you added a lot of mailboxes at once, you'll see a cluster of bars. Hover over a bar to see the breakdown of healthy vs. unhealthy senders on that day.
Trends view
A dual-axis line chart for the selected time period. The purple line tracks total warming email volume; the green line tracks inbox rate (%). Use this to spot when inbox rate drops — usually a sign that content or volume needs adjustment.
Use the period selector (top right of the chart) to view Last 7 / 14 / 30 / 60 / 90 days.
The Warming Senders Table
A full list of every mailbox in warming with these columns:
Column | What it shows |
|---|---|
Mailbox email address. Red ⚠ icon if this sender is flagged as a problem | |
Status | "Initial" (purple) or "Background" (green), with current day/progress |
Progress | Progress bar for Initial warmup senders showing how far through the 14-day ramp |
Inbox Rate | % of warming emails landing in inbox. Color-coded. |
Health | Overall health score. Color-coded. |
Volume | Sent today / Max per day. E.g., "12/50 /day" |
Profile | The sender profile this mailbox is attached to (link) |
Actions per row:
- Hide button — removes the mailbox from the list after background warming completes. Doesn't stop warming — just hides it from this view.
- Settings (gear) icon — opens the sender settings modal to adjust warming speed, daily limits, SMTP settings, and other configuration.
- Chart (bar) icon — expands an inline 30-day history chart for that individual mailbox.
Inbox Placement by Provider
When placement test data is available, the dashboard shows a row of pills indicating inbox placement rates by email provider: Google, Outlook, Yahoo, Zoho, etc. For example: "Google: 97.3% (1,204)" — meaning 97.3% of warming emails sent to Google-hosted addresses landed in the inbox, based on 1,204 messages.
This is the most useful signal for understanding where your mailboxes actually land. If Google shows 94% but Outlook shows 71%, you know to investigate before sending a campaign heavily targeting Outlook-hosted companies.
Expected Result
You can see the warming status of every mailbox, identify which ones are ready to use, and spot any with health problems before assigning them to active campaigns.
Troubleshooting
- Issue: Warming data appears flat (no health score, no inbox rate).
Fix: Confirm the mailbox is connected and actively sending warming emails. Go to Senders → Mailboxes and check the mailbox status. Warming data typically starts appearing within 24 hours of activation.
- Issue: A mailbox shows "Problem" status.
Fix: Click the gear icon on that row to open sender settings. Check if the mailbox connection is still active (SMTP/IMAP auth valid). Common causes: password change on the underlying mailbox, IMAP access disabled, or sending limits hit at the provider.
- Issue: Inbox rate is declining over time.
Fix: Reduce campaign volume on that mailbox and let warming run longer before ramping back up. Also run a placement test to get more diagnostic data.
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Updated on: 17/03/2026
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