Warmup best practices: how long, how fast, and when to launch

Draft — written from product facts + domain knowledge; UI labels to be verified before publishing.

Most deliverability problems trace back to one of three warm-up mistakes: launching too early, ramping too fast, or switching warm-up off once campaigns start. This article gives the numbers that avoid all three and shows where to apply them in OutreachFox.

How long

The Warm up tab shows the start date. Do not count days before the mailbox actually sent.

How fast

Set these in the warm-up profile (Settings → warm-up profiles, or Manage Profiles in the Enable Warm Up dialog):

• Start: 3–5 emails/day for new domains, 10–15 for aged ones.
• Increase: +2–3 per day (Google), +2 per day (Microsoft/Azure), +3–5 (IMAP/SMTP with a good sending host).
• Max: 30–40/day during the pre-launch phase.
• Reply rate: 30–40%.
• After launch: drop the max to 20–25/day and keep it there.

Ramping faster than +5/day is the most common cause of a health score that climbs and then collapses around day 8–10.

When to launch

Launch a mailbox into a campaign only when, on the Warm up tab:

• Health score is 85+ (90+ preferred).
• Inbox placement is 95%+.
• Spam placement is under 5%.
• Bounce rate is 0%.
• The ESP breakdown shows no provider below 85% inbox.
• At least 14 days have elapsed (see table above).

Then:

1. Go to Mailbox, select the mailboxes, and use the bulk actions bar to set campaign emails per day to 20–30.
2. Select them again → Enable Warm Up → choose a reduced profile (max 20–25/day) → Enable Warmer.
3. Add them as Sender Accounts in the campaign and launch.
4. After 7 days, if bounce is under 3% and spam placement is still under 5%, raise the campaign limit to 40–50/day.

Steps: weekly warm-up review

1. Go to Mailbox and sort or scan by health.
2. Open any mailbox under 80 → Warm up tab.
3. Check the ESP breakdown to see which provider is filtering.
4. If spam placement is over 10%, remove the mailbox from campaigns (uncheck it under the campaign's Sender Accounts) and let warm-up run alone for a week.
5. If it does not recover, replace it through Icemail's free mailbox replacement.

Tips

• Stagger new batches. Warming 30 mailboxes on one domain at once creates a volume spike at the domain level; spread them over 2–3 domains.
• Never run warm-up and campaigns from a mailbox whose daily total (warm-up + campaign) exceeds about 70.
• Use provider-matched profiles. Google mailboxes on the Microsoft profile ramp too slowly; Microsoft on Google ramps too fast.
• Keep one or two spare warmed mailboxes per domain so you can swap out a struggling one without pausing the campaign.
• Warm-up cannot compensate for a purchased list with 10% invalid addresses. Verify lists before launch and set the bounce pause at 3%.

Troubleshooting

• Health drops the day campaigns start. Campaign limit too high for the mailbox's age. Halve it and increase weekly.
• Health fine, but campaign replies are low. Deliverability is not the issue; look at copy, targeting and send timing.
• Health never gets above 70. Check DNS and blacklists for the domain; if clean, replace the mailbox.

Related articles

• What is mailbox warmup and how it works in OutreachFox
• Create and customise a warmup profile
• Read the warmup health dashboard
• Troubleshooting warmup (paused, low health score, high spam placement)
• How many mailboxes per domain and domains per campaign (best practice)
• Pre-warmed domains and mailboxes explained