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Warm-up is the difference between landing in inbox and landing in spam. Lemwarm is Lemlist's built-in tool — included in Standard plan and up. Here's how to use it correctly, what to look for in the report, and when you're actually ready to send cold.
Who this is forAnyone setting up new sending mailboxes — first-time outbound, migration from another tool, scaling to additional inboxes. Warm-up is the most-skipped step in cold outbound and the single biggest reason new accounts fail. Take this one seriously.
What you'll need
Step 1
Lemwarm sends and receives emails between thousands of real inboxes in its pool. Your inbox builds a history of legitimate-looking conversations, which trains spam filters to trust it.
Spam filters at Gmail and Outlook score senders based on history: how often does this address send? How often do recipients open, reply, mark as not-spam? An empty-history inbox is treated as guilty until proven innocent.
Lemwarm joins your mailbox to a pool of other Lemwarm users. The pool exchanges natural-looking emails (questions, replies, conversations) with your mailbox. The emails are sent during business hours, opened, replied to, and marked 'important' or 'not spam.'
Over 14-21 days, this conversation history accumulates. Spam filters see consistent engagement and start trusting your mailbox.
Without warm-up, your first cold campaign hits filters with zero history. Even good content goes to spam at 60-80% rate.
After initial warm-up, leave Lemwarm running indefinitely at lower volume — it maintains reputation between sending bursts.
Step 2
Lemlist → Lemwarm → Connect mailbox. Select your already-connected mailbox. Configure starting daily volume.
Open Lemlist → Lemwarm in the left navigation.
Click 'Connect mailbox.' Select the mailbox you previously connected to Lemlist (should appear in dropdown).
Set starting daily volume: 10-15 warm-up emails/day for week 1. Lemwarm will gradually increment to 30-40/day over 21 days.
Set business-hour schedule: 9am-5pm in the mailbox's timezone. This makes warm-up traffic look human.
Enable 'Reply to received emails' — Lemwarm both sends and replies to other warm-up emails, which doubles the engagement signal.
Click 'Start.' Lemwarm begins immediately.
Step 3
The Lemwarm dashboard shows inbox placement %, deliverability per provider (Gmail vs Outlook vs Yahoo), and any warning signs. Check it every day.
Lemwarm → Dashboard. Key metrics:
**Inbox placement %**: target 95%+ by end of week 2. Below 80% after 2 weeks signals deeper issues (DNS, domain age).
**Per-provider placement**: separate scores for Gmail, Outlook, Yahoo. Outlook is consistently the hardest — 85%+ on Outlook is good.
**Spam folder rate**: should drop from 20-40% in week 1 to under 5% by end of week 2.
**Total sent**: tracks daily volume. Should ramp smoothly — flat lines indicate a problem.
If inbox placement is dropping mid-warm-up, pause sending immediately and diagnose. Likely culprits: DNS misconfiguration, domain reputation issue, mailbox provider rate-limiting.
Step 4
Resist the urge to launch your first campaign at day 7. The reputation curve is non-linear — most of the trust-building happens in days 10-14.
Days 1-7: filters are watching. You're being scored on consistency. Don't break the rhythm by sending real cold yet.
Days 8-14: trust accumulates. Inbox placement should climb from 60-70% to 90%+. This is when warm-up is paying off.
Days 14-21: reputation is established. Safe to start small cold sends (20-30/day, climb gradually).
Day 21+: full operational capacity (40-60/day per mailbox).
Common mistake: people see 90% inbox placement on day 9 and start cold sending. The warm-up traffic was making the inbox look healthy. Real cold sends without sustained warm-up will quickly burn the gained reputation.
Step 5
Once you're sending real campaigns, don't turn Lemwarm off. Reduce volume to 10-15/day and let it run as maintenance.
Cold sending burns reputation slightly each day. Warm-up restores it.
Lemwarm settings → reduce daily volume to 10-15/day while you're running real campaigns.
On weekends and during sending pauses, you can bump it back to 30/day to actively rebuild reputation.
Check the dashboard weekly. Any sustained drop in inbox placement is an early warning before deliverability craters.
Pause Lemwarm only if you're permanently retiring the mailbox.
Step 6
Some mailboxes won't warm up regardless. Diagnose at day 7 if placement is below 70%.
Day 7 placement below 70% → check DNS records at mxtoolbox.com. SPF, DKIM, DMARC must all be valid. Any error here means filters can't authenticate you and warm-up traffic is being treated as suspicious.
Domain age under 14 days → you started warm-up too soon after domain registration. Pause warm-up, wait until domain is 30+ days old, restart.
Same domain warm-up failures across multiple mailboxes → the domain is blacklisted. Check at multirbl.valli.org. If blacklisted, request removal from each list (process takes 1-7 days per list).
Specific provider (e.g., Outlook only) failing → that provider has flagged your domain or IP. Contact provider support with your authentication records.
If diagnostics come back clean but warm-up still fails → mailbox provider issue. Try a fresh mailbox on the same domain.
Common mistakes
Sending real cold campaigns during warm-up
What goes wrong: Warm-up traffic was getting your inbox to 85% placement. Cold sends at the same time confuse filters and tank both — you end up worse than no warm-up.
How to avoid: Do NOT send real cold campaigns until day 14+ of consistent warm-up. The discipline pays off.
Skipping warm-up because Apollo/Instantly say they do it built-in
What goes wrong: Other platforms' warm-up varies in quality. Lemwarm is specifically tuned for Lemlist sending patterns. Trusting another tool's warm-up while you're sending via Lemlist creates conflicting signals.
How to avoid: Use the warm-up tool of the platform you're sending from. If you switch platforms, restart warm-up on the new one.
Turning Lemwarm off once cold is running
What goes wrong: Reputation degrades 5-10% per week of unmanaged cold sending. Within 2 months you're back to spam-foldering and rebuilding from scratch.
How to avoid: Run Lemwarm continuously at 10-15/day even during active campaigns. Maintenance is cheap insurance.
Cranking daily volume too fast
What goes wrong: Ramping from 10 to 80/day in 3 days looks fake to spam filters. The very pattern Lemwarm prevents — sudden volume spikes — you create by being impatient.
How to avoid: Let Lemwarm auto-ramp (default is +5 emails/day). If you must override, max +10/day increments with stable 95%+ placement.
Warming up with a misconfigured DNS
What goes wrong: Two weeks of warm-up traffic with bad DKIM trains spam filters to flag you. Worse than no warm-up because now you've accumulated negative reputation.
How to avoid: Always validate DNS via mxtoolbox.com BEFORE starting Lemwarm. All four records (SPF, DKIM, DMARC, MX) must be green.
Recap
Done — what's next
Lemlist deliverability best practices — landing in inbox in 2026
Read the next tutorial
Hand it off
Warm-up is patient work — 2-3 weeks of doing nothing while the system runs. Most founders rush this. A demand-gen specialist enforces the wait, monitors the dashboard daily, and catches deliverability issues before they tank a sending domain. $14-16/hr, included in any ongoing outbound engagement.
See specialist rates
You can warm up multiple, but stagger the starts by 5-7 days. Starting 5 inboxes on the same day on the same domain looks suspicious. Start inbox 1, wait a week, add inbox 2, wait a week, etc.
Not yet. Days 10-14 are when reputation actually consolidates. Sending real cold on day 10 risks resetting the curve. Wait the full 14 days minimum.
If the mailbox has been actively used (sending real human emails, getting replies) for 6+ months, the reputation foundation is there. Still run Lemwarm for 7-10 days as a 'rest the muscle' before scaling cold volume.
Lemwarm runs server-side at Lemlist — no impact on your computer. Sending happens via API to your mailbox, scheduled across business hours. You won't notice it running.
Lemwarm uses Lemlist's pool of warm-up participants — typically 50K+ inboxes. Mailreach has a larger pool with more provider variety. For most teams, Lemwarm is sufficient and saves the cost of running a second tool. Switch only if Lemwarm consistently underperforms after diagnosis.
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