Mailbox Warm-Up Strategy: How to Build Sender Reputation
Before your new inboxes start sending cold outreach, they need to be warmed up. Warm-up is the gradual process of establishing a healthy sender reputation with email providers like Gmail and Outlook. If you skip it or do it too quickly, your emails are more likely to land in spam—or worse, get blocked entirely.
✅ Checklist: How to Warm Up a Mailbox Properly
1. Start Warm-Up Immediately After DNS Is Verified
- As soon as your domain is verified (SPF, DKIM, DMARC, MX), you should start warming the inboxes.
- This gives inbox providers a signal that your domain and mailboxes are legitimate.
- ✅ Mission Inbox starts warm-up automatically when toggled on per mailbox.
💡 You can’t warm up an inbox if DNS isn’t verified. Make sure that’s done first.
2. Use the Recommended Warm-Up Timeline
To protect deliverability, follow this phased approach:
| Week | Action |
|---|---|
| 0 | Setup domain + DNS only |
| 0–3 | Warm-up only (0 real sends) |
| 3–4 | Begin low-volume sending (5–20/day) |
| 4–6 | Increase Gmail-only volume to 30/day |
| 6–12 | Add Gmail & Others, maintain volume |
| 13+ | Begin sending to Outlook. Ramp up to full campaign mode |
🚫 Don’t send cold emails during the first 2–3 weeks.
3. Enable Warm-Up in Mission Inbox
When enabling warm-up in Mission Inbox, tailor your settings to the sequencer you’re using. For platforms like Instantly or Smartlead, follow their recommended warm-up settings. If you're targeting many Outlook users or working with cold lists, enable premium warm-up on Mission Inbox to build reputation faster (note: it uses credits). Mission Inbox defaults to a balanced warm-up, but you can adjust the Gmail-to-Outlook ratio based on your audience. Keeping warm-up enabled is also key if you've had bounce issues or been on blocklists—it helps protect your sender reputation.
Here’s how to activate it:
- Go to your Mailbox List
- Toggle Warm-Up ON for each mailbox
- Credits will automatically be applied (9 per mailbox per month)
🧠 Tip: Turn off warm-up in your sequencer (e.g., Instantly, Smartlead) to avoid double warming.
🧠 Smart Warm-Up with Mission Inbox
Mission Inbox v3 includes a dynamic warm-up engine powered by real-time signals:
- 📈 Adaptive send rate based on reply/bounce rates
- 🔀 Balanced Gmail/Outlook delivery (50/50 split by default)
- 🧠 AI throttle logic that adjusts based on mailbox age and volume
🔁 What If I Skip Warm-Up?
Skipping warm-up leads to:
- 📉 High bounce rates
- 🚫 Instant blocklisting
- 📨 Emails landing in spam
Even worse, your domain reputation can tank—impacting all your inboxes tied to it.
⚠️ Recovery from a damaged domain can take weeks. Warm-up is your best insurance.
🧮 How Many Credits Do I Need?
Each mailbox uses 9 warm-up credits per month.
Your Mission Inbox plan includes 20 credits, and additional credits are charged automatically at $0.40 per credit alongside your renewal.
- 💡 Warming 10 mailboxes = 90 credits = $36/month
📦 Premium Warm-Up vs. Custom Strategy
- ✅ Default: Balanced Gmail and Outlook (50/50)
- 🧪 Custom: Ask us if you want a Gmail-heavy or industry-specific ratio
Just message the team if you need custom distribution.
📞 Still Have Questions?
If your mailbox isn't warming up correctly, or you need help understanding warm-up volume, credits, or results:
➡️ Chat with our team