Best Email Warmup Tools Compared: Instantly vs Warmy vs Mailreach
We tested 5 warmup tools side by side. reply rates, inbox placement, and the real cost of warming up cold email accounts in 2026.
Why Warmup Still Matters in 2026
Email warmup is the process of building sending reputation on a new inbox by gradually increasing email volume with positive engagement signals (opens, replies, removing from spam). Every new cold email account needs warmup before you can safely send outbound campaigns. Skip it, and your emails go straight to spam.
The minimum warmup period is 14 days. Most tools recommend 21-28 days for best results. During this time, the warmup tool sends automated emails between your inbox and a network of other inboxes, generating the positive signals that email providers (Google, Microsoft) use to judge your sending reputation.
We tested the five most popular warmup tools head-to-head on identical fresh inboxes from Puzzle Inbox.
The Tools We Tested
- Instantly Warmup — built into the Instantly sending platform
- Warmy — standalone warmup tool with AI-powered sending patterns
- Mailreach — standalone warmup focused on inbox placement monitoring
- Folderly — warmup plus deliverability consulting
- Lemwarm — built into Lemlist's sending platform
Test Setup
We took 25 fresh (non-warmed) Google Workspace inboxes from Puzzle Inbox, all with identical DNS configuration. We assigned 5 inboxes to each warmup tool. All inboxes started on the same day with default warmup settings. We measured results at Day 14, Day 21, and Day 28.
Results: Day 14 (Minimum Warmup Period)
| Tool | Inbox Placement | Spam Placement | Daily Warmup Volume | Reply Rate (warmup) |
|---|---|---|---|---|
| Instantly | 82% | 12% | 35-40/day | 45% |
| Warmy | 79% | 15% | 20-30/day | 52% |
| Mailreach | 84% | 10% | 30-35/day | 48% |
| Folderly | 80% | 14% | 25-35/day | 40% |
| Lemwarm | 76% | 17% | 20-25/day | 38% |
Results: Day 28 (Full Warmup)
| Tool | Inbox Placement | Spam Placement | Daily Warmup Volume | Reply Rate (warmup) |
|---|---|---|---|---|
| Instantly | 91% | 5% | 40-50/day | 48% |
| Warmy | 88% | 7% | 35-40/day | 55% |
| Mailreach | 92% | 4% | 40-45/day | 50% |
| Folderly | 87% | 8% | 35-40/day | 43% |
| Lemwarm | 84% | 10% | 25-30/day | 41% |
Mailreach and Instantly delivered the best inbox placement results. Warmy had the highest warmup reply rates, which is a positive signal. Lemwarm was the weakest performer across all metrics, likely due to a smaller warmup network.
Pricing Comparison
| Tool | Monthly Cost per Inbox | Standalone? | Free with Platform? |
|---|---|---|---|
| Instantly Warmup | $0 (included with Instantly) | No | Yes (Growth plan+) |
| Warmy | $49/inbox (Starter) or $429/mo for 50 inboxes | Yes | No |
| Mailreach | $25/inbox or $60/mo for 5 inboxes | Yes | No |
| Folderly | $96/inbox or custom pricing for bulk | Yes | No |
| Lemwarm | $0 (included with Lemlist) | No | Yes (Email Pro+) |
The cost difference is dramatic. If you are already using Instantly, warmup is free and performs among the best. Standalone warmup tools add $25-96 per inbox per month, which is often more than the inbox itself costs.
Network Size: Why It Matters
A warmup tool's effectiveness is directly tied to the size of its sending/receiving network. More accounts in the network means more diverse senders and recipients, which creates more realistic engagement patterns that email providers trust.
- Instantly: ~1M accounts in the warmup network (largest)
- Warmy: Proprietary network, estimated ~200K accounts
- Mailreach: ~300K accounts
- Folderly: Undisclosed, estimated ~100K
- Lemwarm: ~100K accounts (smallest major tool)
Instantly's massive network is its biggest advantage. When a million accounts are exchanging warmup emails, the engagement patterns look extremely natural to Google and Microsoft's spam filters. Smaller networks create more repetitive patterns that can eventually be detected.
What Good Warmup Actually Looks Like
Effective warmup is not just about sending volume. The best warmup tools do these things:
- Gradually increase sending volume (not jumping from 0 to 50 overnight)
- Generate genuine replies (not just opens)
- Pull emails out of spam folders (a strong positive signal)
- Vary sending times throughout the day
- Send to a diverse mix of email providers (Gmail, Outlook, Yahoo, etc.)
- Maintain warmup alongside your real campaigns (not just before them)
The Pre-Warmed Alternative
Here is the thing most people miss: if you buy pre-warmed inboxes, you skip the warmup process entirely. Puzzle Inbox offers pre-warmed Google Workspace and Outlook 365 accounts that arrive with established sending reputation. Instead of waiting 14-28 days and paying $25-96/month per inbox for warmup tools, you get inboxes that are ready to send within 24-72 hours.
The math on 50 inboxes over 3 months:
| Approach | Inbox Cost (3 mo) | Warmup Cost (3 mo) | Time to Send | Total |
|---|---|---|---|---|
| Fresh inboxes + Mailreach | $150-300 | $3,750-9,000 | 14-28 days | $3,900-9,300 |
| Fresh inboxes + Warmy | $150-300 | $2,550-7,350 | 14-28 days | $2,700-7,650 |
| Fresh inboxes + Instantly (free) | $150-300 | $0 (need Instantly sub) | 14-28 days | $150-300 + platform |
| Puzzle Inbox pre-warmed | $150-300 | $0 | 24-72 hours | $150-300 |
Our Recommended Warmup Strategy
If you are buying fresh inboxes and using Instantly as your sending platform, use Instantly's built-in warmup — it is free and among the best. If you use a different sending platform (Smartlead, Saleshandy), Mailreach is the best standalone option at a reasonable price.
But the smartest move is to skip warmup entirely. Pre-warmed inboxes from Puzzle Inbox eliminate the warmup cost, the 14-28 day delay, and the risk of burning accounts during the warmup phase. At $0.35 per Outlook inbox and $3-4.50 per Google Workspace inbox, the infrastructure cost is already lower than a single month of standalone warmup tools.