The Best Email Warm-Up APIs - With Real Pricing
You're running 60 inboxes across three client domains, and your warmup provider just quoted you $19.50 per mailbox. That's $1,170/month before you send a single cold email.
The frustration on r/coldemail is loud - people want an email warm-up API with volume-based pricing, not per-inbox math that punishes scale. The core buying decision isn't which tool has the best dashboard. It's whether you're paying per inbox or per volume.
Our Picks
- Best for agencies (50+ inboxes): Mailivery - shared-volume pricing, unlimited mailboxes, $79/mo for 800 emails/day.
- Best per-mailbox option: MailReach - 30k-inbox warmup network, $19.50/mailbox/mo, REST API.
- Verify before you warm: Prospeo - 98% email accuracy, real-time verification API, free tier with 75 verifications/mo.
Pricing at a Glance
Every warmup provider seems allergic to publishing API pricing. Here's what we've actually confirmed.
| Tool | Pricing | Model | API Access | Key Limitation |
|---|---|---|---|---|
| Mailivery | $29-$199/mo | Shared volume | Yes | Per-mailbox cap: 100/day (Starter), 250/day (Pro/Business) |
| MailReach | $19.50/mailbox/mo | Per inbox | Yes (REST) | Scales expensively |
| EmailWarmupAPI.com | $199/mo (100 accts) | Flat | Yes (REST) | No cheaper entry point |
| EmailWarmup.com | $29/mo (standard); API = Enterprise (custom) | Flat | Enterprise only | API gated behind sales |
| Warmy.io | $49 (1 inbox), $99 (3), $249 (15)/mo | Per inbox | Not public | Opaque API pricing |
| Instantly | Free tier; ~$30/mo+ | Bundled | Yes (v2) | Not a standalone API play |
You're spending $79-$1,950/mo warming up inboxes. But warmup can't fix a 35% bounce rate from bad data. Prospeo's real-time email verification API delivers 98% accuracy at $0.01/email - so every warmed-up inbox sends to real people, not spam traps.
Fix the data first. The warmup will actually work.
Top Warmup API Providers Compared
Mailivery
Use this if you're an agency running 50+ inboxes and per-mailbox pricing is killing your margins. Skip this if you only have one or two mailboxes and want maximum daily volume per account.
Mailivery's pricing model is the reason it tops this list. Instead of charging per inbox, you buy a daily warmup volume pool shared across unlimited mailboxes. The Professional plan at $79/mo gives you 800 warmup emails/day - distribute that across 80 mailboxes at 10/day each, or 16 mailboxes at 50/day. Mailivery bumped these limits in 2026 at the same prices, so Starter does 200/day and Business hits 2,500/day at $199/mo.
Let's do the math. 100 inboxes on MailReach costs $1,950/mo. On Mailivery Professional, $79/mo. Their API lets you connect mailboxes, start/pause warmup, and adjust settings programmatically - exactly what agencies embedding warmup into client onboarding need. The tradeoff is per-mailbox daily caps: 100/day on Starter, 250/day on Professional and Business. That limits single-inbox power users but doesn't matter for multi-inbox setups where you're spreading volume thin anyway.
MailReach
MailReach runs a 30k real human inbox network - the biggest any warmup provider publishes. Network size matters because warmup effectiveness depends on engagement diversity; if all your warmup interactions come from the same cluster of inboxes, mailbox providers catch on. Their AI algorithm handles ramp scheduling, delivering up to 100 warmup emails/day per mailbox with 67% average open rates.
The REST API covers what developers need: connect mailboxes, track deliverability signals, and get Slack/webhook alerts when reputation scores shift. It works with Gmail, Outlook, Mailgun, Brevo, Amazon SES, SendGrid, and any SMTP provider. At $19.50/mailbox/mo with custom rates for 100+ mailboxes, it's the right pick for teams running fewer than 50 inboxes who want the strongest warmup network available. Beyond that threshold, the per-inbox costs add up fast.
EmailWarmupAPI.com
A dev-first option with a single, clear price: $199/mo for 100 email accounts with full REST API access, webhooks, and native IMAP/SMTP support. Each account gets 100 positive engagements/day plus spam pattern analytics. Integrations with Make and Integrately round it out.
No cheaper entry point exists, so this only makes sense if you're running 30+ accounts and want zero dashboard overhead.
EmailWarmup.com
The $29/mo standard plan includes personalized warmup, unlimited deliverability tests, and Google Postmaster integration. They offer a 98% inbox placement guarantee or your money back. Solid budget option, but API access is locked behind Enterprise pricing - which means a sales conversation with no published rates. If you need programmatic control, look elsewhere.
Warmy.io
Plans run $49/mo for 1 inbox, $99/mo for 3 inboxes, and $249/mo for 15 inboxes, with Enterprise as custom. API pricing isn't public. Heavy on integrations, light on automation transparency. Expect a sales conversation before you can fully automate anything.
Instantly
Warmup comes bundled with Instantly's outreach platform - free tier available, paid from ~$30/mo/user. They claim a 1M+ account deliverability network with headless-browser engagement signals, which is impressive scale. They also have an API v2 with deliverability endpoints like inbox placement tests and blacklist reports, but warmup-specific start/stop endpoints aren't clearly surfaced in the docs. Better as a full-platform buy than a standalone warmup integration.
Per-Inbox vs Shared Volume
This is the decision that actually matters.
Per-inbox pricing (MailReach, Warmy, most others) works fine under ~30 mailboxes. Beyond that, costs compound fast - and this is exactly the frustration r/coldemail users keep venting about. One thread we found had an agency owner calculating $3,900/mo just for warmup across 200 inboxes. That's absurd.
Shared-volume pricing (Mailivery) flips the model. You pay for total daily warmup capacity regardless of how many mailboxes you connect. For agencies and multi-inbox cold email setups, the choice is obvious.
Here's the thing, though: most teams overspend on warmup and underspend on data quality. We've seen this pattern repeatedly. A $79/mo Mailivery plan paired with verified contact data will outperform a $1,950/mo MailReach setup sending warmup emails from inboxes that also blast unverified prospect lists. Fix the data first, then warm the inboxes.
Pre-Warmup Checklist
Before connecting a single inbox to any warmup API, nail these fundamentals:
- SPF record - one per domain, published in DNS.
- DKIM - 2048-bit key minimum.
- DMARC - start with
p=none(monitor mode), tighten later. - Match warmup to outreach volume - if you send 30 cold emails/day from a mailbox, run 30 warmup emails/day on it.
- Watch complaint rates - Gmail's spam complaint ceiling is 0.3%, but aim for under 0.1%.
- Give it time - plan for 2+ weeks of warmup before launching campaigns. Start at 5-10 emails/day and ramp gradually.
Steps 1-4 aren't optional. We've watched teams skip DMARC or send to unverified lists and wonder why warmup isn't "working." Warmup can't fix what authentication and bad data already broke.
Agencies scaling 50+ inboxes need more than shared-volume warmup - they need verified contacts that protect domain reputation. Prospeo's API returns 92% match rates with 5-step verification, catch-all handling, and spam-trap removal built in. 75 free verifications/mo, no sales call required.
Stop warming inboxes that bounce. Verify your lists first.
FAQ
How long does email warmup take?
Plan for at least 2 weeks before sending campaigns. A realistic ramp: Week 1 at 5-10 warmup emails/day, Week 2 at ~20/day, Week 3 at 30-50/day targeting 25%+ reply rates on warmup threads, Week 4 at your target volume with stable inbox placement.
IP warmup vs mailbox warmup - what's the difference?
IP warmup builds reputation for a sending IP address - relevant for transactional email through providers like Mailgun or SendGrid. Mailbox warmup builds reputation for a specific inbox - relevant for cold outreach via Gmail or Outlook. If you're doing cold email, you need mailbox warmup.
Does warmup alone fix deliverability?
No. If your prospect list has a high bounce rate, warmup can't compensate. Verify emails first - catch invalids and spam traps before they torch your sender score. Warmup and verification are complementary; skipping either undermines the other.
What's the cheapest email warm-up API for 100+ inboxes?
Mailivery's Business plan at $199/mo covers unlimited mailboxes with 2,500 warmup emails/day - roughly $2/inbox at 100 mailboxes. MailReach would cost $1,950/mo for the same count. For high-inbox-count setups, shared-volume pricing wins by a wide margin.