Best Email Warmup Tools In 2026 - Which One Should You Actually Use?

We've sent roughly 8,000 emails a month across 20+ domains for a few years now, and every single one of those domains started life going through some kind of warmup. Before that ramp-up mattered to us, warmup was just a checkbox we clicked without thinking about it. Once we were running that many domains at once, it became one of the few things that can quietly tank an entire campaign if you get it wrong — cold domain, no warmup, straight to spam, no idea why replies stopped coming in.

Here's the TLDR: for most people reading this, the best email warmup tool is the one that's already sitting inside your sending platform for free. We run Instantly's built-in warmup on every domain we own & it's included at no extra cost on every plan — that's been true for us for about four years now. If you're already paying for Instantly, Smartlead, or Lemlist, you probably don't need a standalone warmup tool at all. Where standalone tools like Mailreach, Warmup Inbox, or TrulyInbox actually earn their keep is narrower: you're sending from a platform with weak or no warmup, you want spam-placement testing that's independent of your ESP, or you're an agency juggling client domains across multiple sending tools & want warmup billed separately. Read on & figure out which camp you're in.

What Warmup Actually Does (And Why People Argue About It)

Warmup tools connect a mailbox to a network of other mailboxes, send it low volumes of email, get those emails opened, replied to, & pulled out of spam if they land there, & gradually ramp the sending volume up as the "reputation" signals build. The idea is you're teaching Gmail or Outlook that this is a real human mailbox having real conversations before you point 500 cold emails a day at it.

Where it gets genuinely contentious is network quality. A tool with a small, static pool of seed accounts produces engagement that looks the same every time — same accounts, same reply patterns, same timing. Mailbox providers are good at spotting that now. A tool with a large, constantly rotating network of real active accounts produces engagement that looks more organic, which is the entire point. This is exactly why a cheap warmup add-on bolted onto a small platform can genuinely do less for you than a warmup engine that's been running at scale for years — the network behind it is the product, not just the automation on top.

The Elephant In The Room - What Google (And Microsoft) Actually Did

We're not going to pretend this doesn't exist, because it's the first thing anyone doing real research on warmup tools runs into. On January 31st, 2023, GMass — at the time the most popular email warmup service around, running warmup across more than 80,000 accounts — shut its warmup feature down entirely. Not by choice. Per GMass's own account of what happened, Google told them flat out: shut down the warmup system or lose Gmail API access altogether. Google's stated position was that warmup, as a category, "puts strain on their systems in service of fooling their systems" & that it violates their terms of service — & GMass's founder said Google made clear they intended to apply the same pressure to other warmup providers down the line.

What actually got cut off was Gmail API access — the direct, programmatic hook that let GMass manipulate accounts in bulk. Nearly every warmup tool on the market today, including every tool in this list, works through standard SMTP/IMAP connections instead — the same access method any normal email client uses to check & send mail. That distinction is why warmup as a category didn't die in 2023 the way GMass's implementation did. But we'd be lying if we told you that distinction makes warmup risk-free. Google's stated objection was to the concept of artificially manufactured engagement, not just to one API. GMass's own founder was skeptical that switching to IMAP would fully dodge future enforcement, & we haven't seen anything since to prove him wrong.

Then in 2025, Microsoft added its own layer on top of this, & it's a bigger deal for anyone doing cold email than most people realize. Per Microsoft's own Tech Community post, starting May 5th, 2025, Outlook began enforcing SPF, DKIM, & DMARC authentication for high-volume senders. Domains that don't meet the bar don't get deferred to spam anymore — they get hard-rejected outright, with a 550 5.7.515 error, meaning the email never reaches the recipient at all. That's not a warmup issue specifically, it's an authentication issue, but it's part of the same trend: both Google & Microsoft have gotten stricter about deliverability enforcement, not looser, & that trend line matters when you're picking a tool in 2026.

Our honest read, after running warmup on hundreds of domains: it still works, & we still use it on every domain we own. But "warmup" isn't a magic switch you flip & forget. Pair it with real SPF/DKIM/DMARC setup, favor tools with large & diverse networks over cheap ones with tiny pools, & don't treat a warmed-up domain as an excuse to skip list hygiene. The tools below range from "included free, use it" to "dedicated specialist, pay per inbox" — here's how we'd sort them.

Instantly Warmup

This is what we actually run. Instantly's warmup is unlimited on every single plan — Growth at $47 a month (about $37.60 on annual billing), Hypergrowth at $97, or Light Speed at $358 for the highest-volume senders. Unlimited email accounts + unlimited warmup on all of them. That's the structural difference between Instantly & most of the tools on this list: you're not paying per inbox, so scaling means adding more domains, not more line items on your bill. Our biggest complaint back when we started on Instantly wasn't warmup at all — it was contact management, which they've since fixed with dynamic lists & tagging. Warmup itself has quietly just worked for four years running. We wrote a full breakdown of how it's set up in our guide to warming up emails with Instantly, & the full Instantly review if you want the platform-wide picture.

Right for you if: you're sending (or about to send) from Instantly anyway, or you're comparing sending platforms & want warmup to be a non-issue rather than a line item.

Lemwarm (Lemlist)

We actually ran Lemlist — & lemwarm specifically — for about six months before switching to Instantly. We liked it! The UI was colorful in a way that made the deliverability data easier to actually look at, & lemwarm did its job. What pushed us off Lemlist wasn't warmup, it was scaling costs as we added people & sending volume. Today, lemwarm comes bundled free into every Lemlist plan — Email Pro runs $69 a month ($55 on annual billing), Multichannel Expert runs $109 a month ($87 annual), per Lemlist's own pricing page. If you want lemwarm without the rest of Lemlist's sequencing suite, standalone plans exist too, priced around $29 to $49 per inbox per month depending on the tier, though Lemlist's own site no longer lists these directly — that pricing comes from third-party trackers, so treat it as a starting point & confirm before you buy.

Right for you if: you want Lemlist's multichannel sequencing (LinkedIn + email) alongside warmup, not just warmup on its own.

Smartlead Warmup

Smartlead is a high-volume sending platform we've evaluated closely (a lot of agencies compare it directly against Instantly, & we get why — it's a legitimate option). Warmup is included free, but only on the two highest tiers: Unlimited Smart at $174 a month & Unlimited Prime at $379. On the two entry tiers — Base at $39 & Pro at $94 — warmup isn't included, it's a $59/mo add-on, which changes the math considerably if you're not already planning to be on one of the top plans. Annual billing knocks about 17% off across the board, per Smartlead's own pricing page.

Right for you if: you're already sending from Smartlead on one of the Unlimited tiers — at that point warmup is free the same way it is on Instantly. If you're on Base or Pro, do the math on the add-on before assuming it's cheap.

Warmup Inbox

Warmup Inbox is a dedicated specialist — it doesn't send cold email itself, it just warms mailboxes for whatever platform you're actually sending from. Pricing is straightforwardly per-inbox: Basic at $15 a month, Pro at $49, Max at $79, with roughly 20% off if you commit annually. That's fine at small scale. Run the math at our scale, though — 20+ domains — & even the Basic tier alone would run $300 a month just for warmup, before you've sent a single cold email. That's the tradeoff with any per-inbox specialist tool: simple to understand, expensive to scale.

Right for you if: you're on a platform with no built-in warmup at all & you're only running a handful of inboxes, so the per-inbox math stays reasonable.

Mailreach

Mailreach pairs warmup with spam-placement testing in one subscription, which is its real differentiator — you're not just warming a mailbox, you're periodically checking exactly where your emails land (primary, promotions, spam) across multiple providers. Pricing is tiered per mailbox, starting around $19.50-25 a month depending on how many mailboxes you're warming (it gets cheaper per seat as you add more), with roughly 20% off on annual billing & a set number of spam-test credits bundled in.

Right for you if: you specifically want ongoing, independent spam-placement testing bundled with warmup, decoupled from whatever your sending platform's own health scoring tells you.

Warmforge (Salesforge Ecosystem)

Warmforge is the warmup tool built into the Salesforge sending ecosystem, but it also sells standalone slots at $10 per mailbox per month, dropping with quarterly & annual commitments. It markets itself explicitly on a quality-over-quantity pitch — a per-mailbox "heat score" you're meant to get to 85-100 before launching real campaigns, plus a deliverability-boost feature that pulls warmup emails back out of spam automatically. If you're already a Salesforge subscriber, Warmforge slots are unlimited & included at no extra cost, per their own pricing page — which mirrors exactly the "warmup bundled with your sender" model we like about Instantly, just inside a different ecosystem.

Right for you if: you're already sending through Salesforge (free warmup, same logic as staying inside your platform), or you want a standalone tool built specifically around mailbox-level health scoring rather than raw volume.

TrulyInbox

TrulyInbox flips the per-inbox model on its head — every paid plan connects unlimited mailboxes, & you pay based on total daily warmup email volume instead. Starter is $29 a month for 200 warmup emails a day across however many inboxes you connect, Growth is $99 for 1,000/day, Scale is $199 for 3,000/day, with higher custom tiers above that. There's also a genuinely free plan — one account, 10 warmup emails a day — enough to keep a single low-volume inbox ticking over.

Right for you if: you've got a lot of inboxes but relatively light volume per inbox — the inverse of the Warmup Inbox / Mailreach math, where connecting more mailboxes doesn't automatically cost you more.

Pricing - The Real Difference

Tool	Starting Price	Warmup Included Free?	Pricing Model
Instantly	$47/mo (Growth)	Yes, unlimited on every plan	Flat fee, unlimited accounts
Lemwarm / Lemlist	$69/mo (Email Pro)	Yes, bundled in every Lemlist plan	Flat fee per plan
Smartlead	$39/mo (Base)	Only on Unlimited Smart ($174) & Prime ($379); +$59/mo add-on on Base/Pro	Tiered plan + add-on
Warmup Inbox	$15/inbox/mo (Basic)	No — standalone specialist	Per inbox
Mailreach	~$19.50–25/mailbox/mo	No — standalone specialist	Tiered per mailbox
Warmforge	$10/slot/mo	Free & unlimited with Salesforge subscription	Per slot, or bundled
TrulyInbox	$29/mo (Starter), free tier available	No — standalone specialist	By daily email volume, unlimited inboxes

Which One Is Right For You?

Pick whatever's bundled into your sender if you're already committed to a platform. If you're sending from Instantly, Smartlead's top tiers, or Lemlist, you're paying for warmup already whether you use it or not — so use it, & skip the standalone tools entirely. This is genuinely most of the market, & most people asking "what's the best warmup tool" are really asking a question their sending platform already answered for them.

Pick a standalone specialist if your sender's warmup is weak, absent, or you want spam-placement testing decoupled from your ESP's own scoring. That's Mailreach or Warmup Inbox if you're running a manageable number of inboxes, or TrulyInbox if you've got a lot of mailboxes at lower volume each. Just run the actual math on your inbox count before you commit — per-inbox pricing that looks cheap at 3 mailboxes stops looking cheap at 20.

Pick Instantly specifically if you're evaluating sending platforms & warmup cost is part of that decision. This is where the unlimited-on-every-plan structure actually changes the math versus Instantly's alternatives — you're not adding a warmup line item every time you add a domain, & for an agency running dozens of client domains like we do, that adds up fast. We've covered the broader landscape in our best cold email tools roundup if warmup is just one piece of a bigger platform decision for you.

Of course all of this is downstream of your actual sending setup, domain count, & how aggressively you're scaling. We've been running warmup on every domain we own for about four years now without a single "why did this domain die" mystery we couldn't trace back to something else — bad copy, a bad list, or skipping authentication setup, never the warmup itself. Regardless of what you use, we hope this helped you sort out where you land — best of luck & happy emailing!