Full disclosure: we run GTM Bud, a done-for-you outbound platform, and we have tested every tool on this list across live campaigns. Some links below may be affiliate links. Our opinions are based on real usage across 4,000+ campaigns at Referral Program Pros and GTM Bud, not vendor promises.
Email warm-up is the most boring part of cold outreach and also the part that breaks everything else if you get it wrong. A mailbox with no sending reputation lands in spam. A mailbox with a damaged reputation drags your entire domain down with it.
We have tested standalone warm-up tools, bundled warm-up inside outbound platforms, and the “just send slowly and hope for the best” approach. This is what actually works in 2026.
Quick comparison
| Tool | Starting price | Network size | Standalone or bundled | Best for |
|---|---|---|---|---|
| Instantly Warmup | 30 dollars/mo (with Instantly) | 500K+ | Bundled | Teams already on Instantly |
| Warmbox | 15 dollars/mo per inbox | 35K+ | Standalone | Budget-conscious standalone warm-up |
| Mailreach | 25 dollars/mo per inbox | 20K+ | Standalone | Deliverability monitoring and scoring |
| Lemwarm | 29 dollars/mo (with Lemlist) | 20K+ | Bundled | Teams already on Lemlist |
| WarmupInbox | 22 dollars/mo per inbox | 15K+ | Standalone | Simple setup, no extras |
| Folderly | Custom pricing (from 120 dollars/mo) | Undisclosed | Standalone | Enterprise deliverability management |
| Smartlead Warmup | 39 dollars/mo (with Smartlead) | Undisclosed | Bundled | High-volume multi-inbox setups |
| TrulyInbox | Free tier available, paid from 6 dollars/mo | 10K+ | Standalone | Testing warm-up on a tight budget |
What email warm-up actually does and why it matters
Email warm-up is a process of gradually building a mailbox’s sending reputation by exchanging emails with a network of other real inboxes. The warm-up tool sends emails from your inbox to other users in its network, and those recipients automatically open, reply to, and mark those messages as important. This creates a pattern of positive engagement that email providers like Gmail and Outlook use to determine whether future emails from your address belong in the primary inbox or the spam folder.
The reason warm-up exists is that email providers track reputation at the mailbox and domain level. A brand-new mailbox on a brand-new domain has zero history. If the first thing that mailbox does is send 100 cold emails, providers flag it immediately. Warm-up creates a baseline of trusted activity before you start outbound.
For a deeper look at the mechanics, see our complete warm-up guide. For broader deliverability strategy, our cold email deliverability guide covers DNS records, sending limits, and content optimization beyond warm-up.
How we evaluated
We assessed each tool against five criteria based on what actually affects campaign performance:
- Network size. Larger peer-to-peer networks produce more diverse engagement signals. A 500K-inbox network generates interactions from a wider range of providers, IPs, and geographies than a 10K network. This diversity matters because email providers look for natural engagement patterns.
- Deliverability impact. We tracked inbox placement rates before, during, and after warm-up across Google Workspace and Microsoft 365 mailboxes. The question is simple: does using this tool measurably improve where your emails land?
- Ease of setup. How long does it take from account creation to first warm-up email sent? Some tools require DNS changes, SPF/DKIM configuration, and manual inbox connection. Others connect via OAuth in under two minutes.
- Reporting and diagnostics. Can the tool tell you when your reputation drops, which providers are flagging you, and whether your warm-up is actually working? A tool that runs silently without feedback is nearly useless.
- Pricing. Most outbound teams run multiple inboxes. A tool priced at 25 dollars per inbox per month becomes 250 dollars per month for a 10-inbox setup. We evaluated both per-inbox and platform-level pricing.
Detailed reviews
Instantly Warmup: best for teams already using Instantly
What it does: Instantly Warmup is bundled with the Instantly outbound platform and uses a network of over 500,000 real inboxes to generate warm-up interactions. It runs automatically once you connect a mailbox and requires no separate configuration. Warm-up runs alongside your campaigns, maintaining reputation while you send.
What works well:
- Largest warm-up network of any tool on this list, which produces the most diverse engagement signals
- Zero additional setup if you already use Instantly for campaigns
- Built-in deliverability dashboard that tracks inbox placement by provider in real time
Where it falls short:
- You cannot use it without an Instantly subscription, so it is not an option for teams on other outbound platforms
- Warm-up settings are limited compared to standalone tools — you get basic volume controls but not granular scheduling or provider-specific targeting
Pricing: Included with Instantly plans starting at 30 dollars per month. The Growth plan at 78 dollars per month adds unlimited warm-up accounts.
Verdict: The best bundled warm-up tool in 2026 if you are already on Instantly — the network size alone makes it hard to beat, but you are locked into the platform.
Warmbox: best standalone warm-up for the price
What it does: Warmbox is a standalone warm-up platform that connects to your mailbox via SMTP/IMAP and generates interactions from a network of over 35,000 inboxes. It offers multiple warm-up “recipes” that simulate different engagement patterns, from casual conversation threads to business-style email exchanges.
What works well:
- Multiple warm-up recipes let you match the interaction style to your actual sending patterns
- Clean dashboard with daily reputation scoring and provider-level breakdown
- Connects to any email provider, not just Google and Microsoft
Where it falls short:
- Network is significantly smaller than Instantly’s, which means less diversity in engagement signals
- The recipe system adds complexity that may not meaningfully improve results over simpler tools
Pricing: Solo plan at 15 dollars per month for one inbox. Premium at 69 dollars per month for three inboxes with priority warm-up. Enterprise pricing available for larger teams.
Verdict: The best standalone warm-up tool in 2026 for teams that want dedicated warm-up without committing to an outbound platform. The price-to-quality ratio is the strongest in this category.
Mailreach: best for deliverability monitoring and scoring
What it does: Mailreach combines warm-up with a detailed email reputation scoring system. Beyond generating warm-up interactions from its 20K+ network, it runs continuous deliverability tests that show exactly where your emails land across Gmail, Outlook, Yahoo, and other providers. The reputation score updates daily and gives you a single number to track.
What works well:
- Reputation scoring is the best in class — the daily score with provider-level breakdown gives you a clear signal of whether things are improving or degrading
- Deliverability tests run seed emails to actual inboxes and report whether they landed in primary, promotions, or spam
- Actionable alerts when your reputation drops below thresholds you set
Where it falls short:
- Smaller network than Warmbox or Instantly, so the warm-up interactions themselves are less diverse
- The interface can feel cluttered because it tries to surface a lot of data at once
Pricing: Starter at 25 dollars per month per inbox. Custom pricing for 10+ inboxes.
Verdict: If your primary concern is monitoring and maintaining deliverability rather than just running warm-up on autopilot, Mailreach is the right choice. The scoring system alone is worth the price for teams that run high-volume outbound.
Lemwarm: best for Lemlist users
What it does: Lemwarm is the warm-up feature built into Lemlist. It connects your sending accounts to a network of 20,000+ Lemlist user inboxes and generates automated interactions that mimic natural email behavior. Like Instantly’s warm-up, it runs in the background while your campaigns send.
What works well:
- Seamless integration with Lemlist campaigns, automatically adjusting warm-up volume based on your sending activity
- Provides a deliverability score and basic reporting
- “Smart” warm-up algorithm that adapts to your inbox’s current reputation
Where it falls short:
- Limited to Lemlist subscribers, so it is not a standalone option
- The 20K network is adequate but not large enough to compete with Instantly’s 500K+ network on diversity alone
Pricing: Included with Lemlist plans starting at 29 dollars per month. Available on all paid tiers.
Verdict: Does the job if you are on Lemlist, but it is not a reason to choose Lemlist. For a broader look at Lemlist and its competitors, see our Lemlist alternatives breakdown.
WarmupInbox: best for simple, no-frills warm-up
What it does: WarmupInbox is a straightforward standalone warm-up tool that connects via SMTP/IMAP and generates interactions from a network of 15,000+ inboxes. It focuses on doing one thing — warming up your mailbox — without layering on campaign tools, CRM integrations, or deliverability suites.
What works well:
- Setup takes under five minutes and requires no technical knowledge beyond your SMTP credentials
- Clean, minimal interface that shows warm-up progress without overwhelming you with data
- Consistent performance — it has been around since 2020 and the core product is stable
Where it falls short:
- Reporting is basic compared to Mailreach or Warmbox — you get warm-up volume stats but not detailed provider-level deliverability scoring
- Smaller network limits the diversity of engagement signals
Pricing: 22 dollars per month per inbox. Volume discounts available for 10+ inboxes.
Verdict: A reliable option for teams that want warm-up running without thinking about it. Not the most powerful, but among the most consistent.
Folderly: best for enterprise deliverability management
What it does: Folderly positions itself as an enterprise deliverability platform rather than just a warm-up tool. It combines warm-up with DNS configuration auditing, blacklist monitoring, content analysis, and dedicated deliverability consulting. The platform targets companies sending at high volume who need comprehensive inbox placement management.
What works well:
- Comprehensive deliverability audit that goes beyond warm-up to cover DNS records, content triggers, and blacklist status
- Dedicated support and consulting, which is rare in this space
- Template analysis tool that scans your email copy for spam trigger words and formatting issues
Where it falls short:
- Pricing is dramatically higher than every other tool on this list, starting at 120 dollars per month and scaling into custom enterprise contracts
- Overkill for small teams running fewer than 10 inboxes — the consulting and enterprise features add cost without proportional value at that scale
Pricing: Plans start at 120 dollars per month. Enterprise pricing is custom and typically requires annual commitment.
Verdict: If you are a larger organization with a dedicated email operations team and budget to match, Folderly provides a level of deliverability management that standalone warm-up tools cannot. For small outbound teams, the cost-to-value ratio does not make sense.
Smartlead Warmup: best for high-volume multi-inbox setups
What it does: Smartlead bundles warm-up with its outbound platform, which is built specifically for agencies and teams managing large numbers of sending accounts. The warm-up runs automatically across all connected inboxes and is designed to scale to hundreds of accounts without per-inbox pricing becoming prohibitive.
What works well:
- Unlimited warm-up accounts on all plans, which is a significant cost advantage for teams running 20+ inboxes
- Master inbox and unified reporting across all sending accounts
- Auto-rotation between warm-up and campaign sending to maintain reputation while sending at volume
Where it falls short:
- Warm-up network size is not publicly disclosed, which makes it hard to compare interaction diversity against Instantly or Warmbox
- The platform has a steeper learning curve than standalone warm-up tools — you are onboarding to a full outbound platform, not just connecting a warm-up service
Pricing: Basic plan at 39 dollars per month with unlimited warm-up. Pro at 94 dollars per month with additional campaign features. Custom pricing for agencies.
Verdict: The unlimited warm-up pricing makes Smartlead the most cost-effective option for teams managing many inboxes. If you are comparing outbound platforms more broadly, see our Instantly alternatives roundup and cold email software comparison.
TrulyInbox: best for testing warm-up on a budget
What it does: TrulyInbox is a lightweight warm-up tool with a free tier that lets you warm up one inbox at a basic level. Its paid plans add more daily interactions and access to a larger portion of its 10,000+ inbox network. It is the most accessible entry point for teams that have never used warm-up before.
What works well:
- Free tier actually works for a single mailbox, which is rare — most “free” warm-up offerings are trials with hard time limits
- Paid plans are the cheapest on this list at 6 dollars per month per inbox
- Simple enough that anyone can set it up without reading documentation
Where it falls short:
- Smallest network on this list, which limits the quality and diversity of engagement signals
- Reporting is minimal — you get basic open/reply stats but no deliverability scoring or provider-level breakdown
Pricing: Free for one inbox with limited daily interactions. Paid plans from 6 dollars per month per inbox.
Verdict: The right starting point if you want to test whether warm-up makes a difference before committing to a paid tool. Not sufficient for teams running production outbound campaigns at any real scale.
How to choose the right warm-up tool
The decision depends on three factors: your existing tools, your inbox count, and your budget.
If you already use an outbound platform: Start with the built-in warm-up. Instantly, Lemlist, and Smartlead all include warm-up that is good enough for most teams. Adding a standalone tool on top creates unnecessary complexity and cost unless you have specific deliverability problems that the bundled tool is not solving.
If you run 1-5 inboxes and want standalone warm-up: Warmbox or Mailreach. Choose Warmbox if you want clean, reliable warm-up at the lowest cost. Choose Mailreach if deliverability monitoring and scoring matter more to you than raw warm-up volume.
If you run 10+ inboxes: The per-inbox pricing of standalone tools adds up fast. Smartlead’s unlimited warm-up or Instantly’s Growth plan become significantly more cost-effective at scale.
If you want to test before committing: TrulyInbox’s free tier or Warmbox’s Solo plan at 15 dollars per month are low-risk starting points.
If warm-up complexity is a dealbreaker: GTM Bud manages email infrastructure including warm-up as part of its done-for-you campaigns. You never touch warm-up settings, DNS records, or inbox rotation — it is handled as part of the service.
Common warm-up mistakes
Stopping warm-up when campaigns start. Warm-up is not a one-time setup step. It needs to run continuously alongside your outbound sending. Cold emails generate negative signals (low open rates, spam reports) that warm-up counteracts. Turning it off once you start campaigns removes that counterbalance exactly when you need it most.
Warming up too many inboxes on the same domain. If you create five mailboxes on one domain and warm up all of them simultaneously, you are concentrating all engagement signals on a single domain. If anything goes wrong, the entire domain’s reputation takes the hit. Spread inboxes across multiple domains so a problem with one does not cascade.
Ignoring warm-up reporting. Running warm-up on autopilot without checking deliverability scores is like running ads without checking conversion rates. If your inbox placement is declining despite warm-up, something else is wrong — your content is triggering spam filters, your DNS records are misconfigured, or your sending volume exceeds what your reputation can support. The warm-up tool’s reporting exists to surface these problems early.
Using warm-up as a fix for bad sending practices. Warm-up builds and maintains reputation. It cannot override the damage from sending 500 cold emails per day from a single inbox, using spammy subject lines, or emailing purchased lists with high bounce rates. If your core sending practices are broken, warm-up is a bandage on a structural problem.
The bottom line
The best standalone warm-up tool in 2026 is Warmbox for its combination of price, network quality, and reporting. The best bundled warm-up is Instantly Warmup because of its 500K+ network size. The best warm-up for deliverability monitoring is Mailreach because of its reputation scoring system.
For most small outbound teams, the warm-up tool bundled with your outbound platform is sufficient. Switch to standalone warm-up only if you see deliverability problems that your current tool is not catching or fixing. And if you would rather not manage warm-up at all, platforms like GTM Bud handle it as part of a fully managed outbound service.
Whatever you choose, the two non-negotiable rules are: start warm-up at least two weeks before your first campaign, and never turn it off while you are sending.