Warmy vs Folderly vs MillionVerifier: Best Email Deliverability Tools in 2026

Cold email dies in the spam folder, not in the subject line. You can write the perfect sequence, but if your domain reputation is weak or your list is full of dead addresses, Gmail and Outlook never show your work to anyone. Deliverability is the unsexy bottleneck of every outbound motion — and the three tools in this comparison attack it from different sides. Warmy and Folderly warm your sending reputation; MillionVerifier verifies the list itself before you send. Here is how the full deliverability stack shakes out, which half of it you actually need, and what each costs at agency scale.

Our short take: for most senders, the smartest money is MillionVerifier for list hygiene plus the warmup bundled into your sending platform — reserving Warmy or Folderly for diagnosing an existing spam problem. Keep reading for the exact math.

Quick verdict

If your emails are already landing in spam and you don’t know why, go with Folderly — its root-cause diagnosis tells you exactly what’s triggering filters. If you want the deepest per-mailbox warmup analytics on a handful of high-value domains, go with Warmy. If you haven’t verified your list, start with MillionVerifier first — no warmup tool can save a list full of dead addresses, and at about $3.70 per 1,000 verifications it’s the cheapest half of this stack.

Warmy vs Folderly vs MillionVerifier at a glance

Warmy: the deep warmup with agency-hostile pricing

Warmy is the best-known dedicated warmup tool on this list, and the most expensive way to do the job. Its pricing runs per mailbox: Starter at $49/month per mailbox, Business at $129, Premium at $189, and Expert at $279. What you get for that money is a polished warmup engine with genuinely deep diagnostics — per-mailbox health tests, inbox placement tests, spam-score monitoring, and warmup conversations available in 30 languages with topic-matched exchanges that look natural to inbox providers.

In practice, Warmy is built for teams warming a handful of high-value sending domains — think a sales team with three to five mailboxes that need to land in the primary inbox of enterprise buyers. The 4.8/5 G2 rating across several hundred reviews backs up the quality of the warmup engine itself.

The problem is the per-mailbox model at scale. Ten inboxes on the Starter plan costs $490 a month; twenty costs $980. Reviewers repeatedly flag price as the tool’s biggest weakness — it’s the most common negative theme across hundreds of G2 reviews. If you’re an agency or lead-gen shop running dozens of sending inboxes, that math collapses fast, which is exactly why the market has moved toward bundled warmup inside sending platforms.

Warmy pricing (per mailbox, per month): Starter $49 · Business $129 · Premium $189 · Expert $279

Pros:

• Deepest per-mailbox diagnostics of any dedicated warmer, including inbox placement tests
• 30-language warmup with topic-matched conversations looks natural to providers
• 4.8/5 G2 rating; strong support responsiveness
• Integrations with Gmail, Outlook, and SMTP setups

Cons:

• Per-mailbox pricing punishes scale — $490/mo for 10 inboxes on the cheapest tier
• No free tier published; confirm trial availability before paying
• You pay separately for every mailbox, so agency costs compound monthly

Folderly: the spam detective that costs like a retainer

Folderly is less a warmup tool and more a deliverability consultancy in software form. Its headline pricing is about $120 per mailbox per month on monthly billing (drops to $96 per mailbox per month on the annual plan for 1–9 mailboxes, $72 for 10–24, and $56 for 25–99). That’s the most expensive dedicated warmup on the market — but warmup is almost not the point.

Folderly’s differentiator is root-cause analysis. Instead of warming and hoping, it tells you exactly why your emails are hitting spam: content-level triggers, broken DNS authentication, reputation problems, even whether your mail lands in the spam folder or the Promotions tab — a distinction most warmup tools don’t make. Independent testing reports inbox placement around 96% after four weeks, and the free extras are real: Pulse monitoring (real-time domain health checks) and Inbox Insights (two free placement tests a month) cost nothing.

The catch is billing lock-in. Folderly’s warmup runs on annual billing, so five mailboxes commits you to nearly $5,800 a year before you’ve proven the tool works. At 4.8/5 on G2, customers rate it highly — but the product is aimed squarely at funded teams with fewer than ten mailboxes and a spam problem worth paying to diagnose.

Folderly pricing (per mailbox, per month): 1–9 mailboxes: $120 monthly / $96 annual · 10–24: $72 annual · 25–99: $56 annual

Pros:

• Best root-cause spam diagnosis in the category — tells you what triggers filters and how to fix it
• Distinguishes spam vs. Promotions placement, which most tools skip
• Free Pulse monitoring and Inbox Insights starter tier included
• DNS setup help and content analysis with concrete fix steps

Cons:

• Most expensive dedicated warmup per mailbox on the market
• Annual billing required — no month-to-month option on warmup
• No free trial; overkill if you just need everyday warmup without diagnostics

MillionVerifier: the verification half everyone skips

MillionVerifier is the odd one out here — and that’s the point. It doesn’t warm anything. It’s an email verification service that cleans your list before you send, which is the other half of deliverability that warmup tools can’t fix: a warmed domain sending to dead addresses still bounces, and bounces still destroy reputation.

Pricing is refreshingly simple: pay-as-you-go credits at about $3.70 per 1,000 verifications, credits never expire, and new accounts get 100 free credits with no card required. The standout is the risky-email refund — you don’t pay for catch-all, unknown, or risky results, and MillionVerifier refunds your last payment if your hard bounce rate exceeds 4%. For ongoing hygiene, the EverClean add-on continuously re-verifies your list on a monthly subscription.

If you’re comparing cold email platforms, this is the hygiene layer that sits underneath all of them — our lemlist vs Instantly vs Apollo breakdown covers the sending side. Verification is the least glamorous and most cost-effective deliverability spend in this comparison: cleaning a 100,000-address list costs roughly $370 one time, while warming the inboxes that send to it can cost that much every month.

MillionVerifier pricing: ~$3.70 per 1,000 verifications (pay-as-you-go) · 100 free credits for new accounts · credits never expire · risky emails not billed

Pros:

• Lowest cost per address in the deliverability stack — pennies per thousand
• Credits never expire; no subscription required for one-off list cleans
• Risky-email refund and 4% hard-bounce money-back guarantee
• 99%+ claimed accuracy; trusted by 70,000+ businesses per the vendor

Cons:

• Not a warmup tool — it does nothing for sender reputation on its own
• Catch-all handling policies matter at scale; confirm with your own test batch
• Accuracy claims are vendor-reported; run a 1,000-address test before committing volume

Head-to-head: the criteria that decide your deliverability budget

Per-inbox cost at agency scale (10 inboxes): Warmy Starter runs $490/mo; Folderly runs $960/mo monthly ($800 annual-equivalent); MillionVerifier costs $0 recurring — you buy verification credits only when you have a list to clean. On pure cost, verification wins by a mile.

Diagnostic depth: Folderly wins — root-cause spam analysis with fix steps. Warmy is runner-up with per-mailbox placement tests and health scoring. MillionVerifier doesn’t diagnose reputation; it diagnoses list quality, which is a different job.

Free tier: MillionVerifier wins easily — 100 free credits, no card. Folderly offers free Pulse monitoring but no warmup trial. Warmy publishes no free plan.

Billing lock-in: MillionVerifier wins — credits never expire, no subscription required. Warmy is month-to-month per mailbox (flexible but expensive). Folderly requires annual billing, which is the heaviest commitment in this comparison.

Final verdict

These three tools aren’t really competitors — they’re different layers of the same stack, and the right answer is usually two of them, not one.

Warming a few valuable domains: Warmy — deepest per-mailbox analytics, set-and-forget warmup, but only if your inbox count stays small. The moment you cross ~10 mailboxes, bundled warmup from your sending platform becomes the rational choice.

Emails stuck in spam and you don’t know why: Folderly — buy the diagnosis, not just the warmup. Its root-cause analysis justifies the premium when the alternative is months of lost pipeline from a burned domain.

Everyone else — start here: MillionVerifier — verify every list before you send, ever. At a few dollars per thousand with never-expiring credits, it’s the cheapest deliverability insurance in this comparison, and it pairs with whatever sending platform you choose.

For the sending side of the stack, see our comparison of lemlist vs Instantly vs Apollo — the platforms whose bundled warmup often makes a dedicated warmer redundant.

How we compared

We scored these three on per-inbox cost at agency scale (10+ mailboxes), diagnostic and analytics depth, and pricing-model flexibility — weighted heaviest, since per-mailbox warmup pricing punishes exactly the senders who need deliverability most. List-verification cost was included because bounce prevention is half the deliverability equation. Pricing checked against the vendors’ pricing pages and current comparison roundups in October 2026; confirm before you buy.

Frequently asked questions