Warmbly
Open-source cold email platform with warmup, unlimited mailboxes, a unified inbox and a map-based local lead finder, from $29/mo or free to self-host.
From $29/mo 14-day free trial MCP server API
Bottom line
Open-source cold email platform that bundles warmup, unlimited mailboxes, a labelled reply inbox and a map-based local lead finder. Cloud plans price by daily sends from $29 a month with a 14-day free trial, and agencies that want to own the stack can self-host the whole thing free.
Stands out for: It is the only full cold email platform in the directory whose sending, warmup and health rules are public code under Apache 2.0, so an agency can read why a mailbox was slowed or run the whole thing on its own server. Paid plans charge by daily send volume with unlimited mailboxes and no seat fees, and the built-in lead finder turns a drawn map area into named owners with checked addresses ready for a campaign.
Watch out for: Self-hosting is free but its warmup only pairs the mailboxes on your own instance, with no shared pool and community-only support, so for deliverability the paid cloud is the real product. The Starter plan caps you at 150 cold emails a day, and the CRM, API and A/B tests start on the $89 Grow plan. The lead finder reads small business websites, so it suits local and SMB prospecting rather than finding hiring managers at larger companies.
Overview
Warmbly is a cold email platform released as open source under Apache 2.0 by Mindroot Ltd. It connects Google Workspace, Microsoft 365 or any SMTP and IMAP mailbox, checks the domain's SPF and DMARC records, warms each mailbox in a shared pool starting at 10 emails a day, and then sends sequences spread across your mailboxes with a daily cap and spacing for each one.
Replies from every mailbox arrive in one inbox, labelled as interested, out of office, a question or an unsubscribe, and a reply stops the sequence for that contact. Unsubscribes, bounces and complaints are suppressed across the whole workspace, which matters for agencies where several recruiters write to the same market. Inbox placement tests, a deal pipeline, visual automations with AI steps and campaign analytics are built in.
The lead finder searches a map for businesses of a kind inside an area you draw, using OpenStreetMap for free or your own Google Places, Foursquare or Outscraper key. It reads each business website for the people who run it, works out their addresses from the domain's pattern and checks them with the mail server without sending, marking each one confirmed, likely or a best guess. Website reads cost $0.02 each on the cloud.
Cloud plans are priced by daily send volume: Starter $29 a month for 150 cold emails a day, Grow $89 for 3,000, Business $329 for 15,000 and a quoted Enterprise tier, with 20% off yearly and no seat charge. A 14-day trial needs no card. Self-hosting is free with a one-command install, and developers get a REST API, signed webhooks, SDKs for JavaScript, Python and Go, a CLI and a first-party MCP server for AI clients.
Who it's for
Best for
- Staffing agencies giving each recruiter their own warmed mailbox
- Teams that want unlimited mailboxes without per-inbox pricing
- Agencies prospecting local small businesses by area
- Technical teams that want to self-host cold email
Not ideal for
- Teams needing a large B2B contact database built in
- Prospecting named decision makers at enterprise companies
- Non-technical users wanting free deliverability from self-hosting
Key features
Warmup and sending. Connect Google Workspace, Microsoft 365 or any SMTP and IMAP mailbox, warm it in a shared pool and send sequences spread across your mailboxes with a per-mailbox daily cap, 50 by default.
Unified inbox. Replies from every mailbox land in one inbox, already labelled interested, out of office, question or unsubscribe, and a reply stops the sequence.
Map-based lead finder. Draw an area on a map, pull every business of a type inside it, read each website for the people who run it and check their worked-out addresses with the mail server before adding them to a campaign.
Open source and API. The whole platform is on GitHub under Apache 2.0 with a one-command self-host install, plus a REST API, signed webhooks, SDKs, a CLI and a first-party MCP server.
AI features
| What the AI does | Plan |
|---|---|
| Labels every reply as interested, out of office, a question or an unsubscribe | All paid plans |
| Drafts or rewrites sequence steps | All paid plans |
| AI steps in automations that read a reply and act, using only the actions you allow | All paid plans |
Only features named in the vendor's own documentation. Anything sold separately is marked as an add-on.
MCP server
https://api.warmbly.com/v1/mcp
First-party MCP at api.warmbly.com. https://api.warmbly.com/v1/mcp.
Setup steps and live status MCP Directory Check your stack in the MCP readiness checker
Pricing
| Plan | Price | What you get |
|---|---|---|
| Starter | $29/mo | 150 cold emails a day, unlimited mailboxes and warmup |
| Grow | $89/mo | 3,000 a day, adds CRM, A/B variants, API and webhooks |
| Business | $329/mo | 15,000 a day, adds dedicated sign-in address, team roles and audit log |
| Enterprise | Quote | 15,000+ a day, SSO and custom contract |
Four plans priced by daily send volume, all with unlimited mailboxes, unlimited warmup, the unified inbox and analytics: Starter $29/mo (150 cold emails a day), Grow $89/mo (3,000 a day, adds the CRM, A/B variants, API and webhooks), Business $329/mo (15,000 a day, adds a dedicated sign-in address, team roles and audit log) and Enterprise on quote (15,000+ a day, SSO and custom contract). Paying yearly takes 20% off ($23, $71 and $263 a month). No per-seat charge. The 14-day free trial needs no card and allows two mailboxes and 20 cold emails a day. Self-hosting the whole platform is free, but its warmup only pairs your own mailboxes and support comes from the community. Confirm current terms on the vendor site.
Checked 8 Nov 2026. Vendors change prices without notice.
Is Warmbly expensive?
Warmbly starts at $29/mo. We list 148 outreach tools in total. 32 have a free tier, and those with a public price typically start around $49 a month.
- 22 quote-based
- 32 free tier
- 125 public price
Worked out automatically from every outreach listing, so it updates as the directory changes.
Pros and cons
Pros
- Open source, free to self-host
- Unlimited mailboxes and warmup on paid plans
- Map lead finder with checked emails
Cons
- Self-hosted warmup has no shared pool
- Starter capped at 150 emails a day
- CRM and API start on $89 plan
Integrations
Slack HubSpot Salesforce Pipedrive Zapier Make n8n Calendly
What's new at Warmbly
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How Warmbly compares
See all Warmbly alternatives, with what each one does differently and a head to head for every pairing.
| Tool | Free tier | From | MCP | API | Compare |
|---|---|---|---|---|---|
| | – | $29/mo | ✓ | ✓ | |
| | – | $37.60/mo | ✓ | ✓ | Compare |
| | – | $32/mo | ✓ | ✓ | Compare |
 Armada Also aimed at agencies selling to local businesses from map listings and owner lookups, but early access and quote-based, while Warmbly posts prices and adds full sequencing. | – | Quote-based | – | ✓ | Compare |
$37.60/mo MCP API
The best-known cold email platform with warmup and a unified inbox from $37.60 a month, closed source but with a larger lead database and a wider user base than Warmbly.
$32/mo MCP API
Agency-focused cold email with unlimited mailboxes from $32 a month, a closer fit for agencies running many client workspaces, though it cannot be self-hosted.
ArmadaQuote-based API
Also aimed at agencies selling to local businesses from map listings and owner lookups, but early access and quote-based, while Warmbly posts prices and adds full sequencing.
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