Warmbly

Open source alternative to Instantly, Smartlead, Lemlist, Woodpecker and Saleshandy

851 stars
Apache-2.0
Active this week
Last commit today

Last verified Nov 2, 2026

Run cold email campaigns from your own mailboxes, with automatic warmup, a unified inbox, and a built-in CRM. Apache-2.0; self-host or use the cloud.

Visit website GitHub851 Deploy on Hostinger

Read the full breakdownWho it is for, how it works, trade-offs, the quick start and the FAQ

who it's for

Who Warmbly is for#

Sales teams managing 20 or more outbound mailboxes

Warmbly was built for this workflow. Connect every mailbox, let the warmup pool ramp each one, and run multi-step sequences that spread sends across the whole pool at once. The unified inbox handles replies from all accounts in one place, and the CRM board moves interested leads to the next stage without switching tools.

Skip if:

Your team sends fewer than 50 emails per day across all accounts. At low volume, the overhead of a self-hosted platform outweighs the benefit; the free cloud plan covers ten mailboxes with no credit card required.

Growth engineers building self-hosted sending infrastructure

Warmbly's control plane and worker architecture is designed to scale by adding more workers. The REST API and signed webhooks let external systems trigger campaigns and read contact state. The Apache-2.0 licence means the codebase can be forked and extended without restriction.

Skip if:

You need a managed API with per-call billing and no infrastructure responsibility. In that case the Warmbly cloud plan or a transactional email API is a simpler fit.

Operators migrating away from Instantly or Smartlead

Warmbly covers the same core feature set: warmup, multi-step sequences, a reply inbox, and analytics. The self-hosted path eliminates per-mailbox billing. Campaign data and contact lists can be imported via the bulk contact import and API.

Skip if:

You rely on features Warmbly does not yet cover, such as advanced email verification at scale or third-party review integrations. Check the GitHub issues and changelog before migrating a large sending operation.

Compliance-aware teams with data residency requirements

Self-hosting places all email metadata, contact records, campaign history, and credentials on infrastructure the operator controls. Warmbly requires no external services in the default configuration. The data control documentation at docs.warmbly.com covers every store's location and retention window.

Skip if:

Your compliance requirement includes a specific vendor certification such as SOC 2 or ISO 27001. Warmbly does not publish certifications; the managed cloud plan would need to satisfy those requirements separately.

the problem

The problem it solves#

Cold email deliverability is fragile. Every mailbox that shows signs of spam (high bounce rates, missing DMARC records, no warmup history) loses inbox placement at Gmail and Outlook, sometimes within days. Repairing a damaged mailbox takes weeks of careful warmup, during which it cannot send at campaign volume.

Most outreach teams juggle several tools to manage this: a warmup service, a sequencer, and a shared inbox, each with its own billing. Costs stack up quickly at scale. Proprietary platforms that bundle these functions lock your campaign history, contact data, and sending analytics behind a subscription that rises with team size or send volume. Moving away means exporting what the platform allows and rebuilding everything else.

how Warmbly solves it

How it solves it#

Mailbox warmup with placement monitoring

The warmup pool exchanges real email with monitored inboxes, starting at ten messages per day per mailbox and growing gradually. Warmbly tracks inbox placement at Gmail, Outlook, and Yahoo and automatically reduces a mailbox's send volume if its spam rate climbs. Each mailbox shows a live health score and a 30-day ramp history so you can see exactly where it stands before a campaign starts.

Multi-step campaigns with per-mailbox send caps

Build email sequences with any number of steps, set a daily send limit per mailbox, and let Warmbly distribute sends across the pool with randomised spacing between each one. Campaigns stop automatically when a contact replies or unsubscribes, so no manual cleanup is needed. A/B variants are supported per step, with split percentages tracked in real time.

Unified inbox with automatic reply categorisation

Replies from every connected mailbox arrive in one place, labelled automatically as interested, out of office, a question, or an unsubscribe. The thread shows the full conversation history from any mailbox, so sales reps handle replies without switching accounts. Sending from the unified inbox uses whichever mailbox the conversation started on.

Visual automation builder with AI intent steps

A canvas-based automation builder triggers on replies, booked meetings, bounces, and warmup dips. Branches evaluate reply intent, and AI steps can read a reply and decide which path it takes. Each step is testable with a dry run against sample data before it goes live. Integrates with HubSpot, Salesforce, Pipedrive, Slack, Zapier, and n8n.

Built-in CRM with pipelines and deal tracking

Contacts, pipeline stages, deals, tasks, and meeting logs live inside Warmbly. Interested replies can move from the inbox to a deal stage on a CRM board without leaving the tool or opening a separate application. Available from the Grow plan and above on the managed cloud; fully included on self-hosted.

REST API and signed webhooks

A REST API and signed webhooks are included from the Grow plan on the managed cloud and are always available on self-hosted. External systems can trigger campaigns, query contact state, and receive real-time events for every reply, bounce, unsubscribe, and warmup dip. The API reference and webhook signature verification steps are documented at docs.warmbly.com.

strengths · trade-offs

Strengths and trade-offs#

Strengths

No per-mailbox fees on self-hostedWarmbly's Apache-2.0 licence places no restrictions on the number of mailboxes or users for self-hosters. Teams running 50 or 500 mailboxes pay only for the server. This differs from Instantly and Smartlead, which tier pricing by mailbox count; at 50 mailboxes those costs can exceed $100 per month before CRM or API access is unlocked.
Outbound mail leaves through the mailbox's own providerWorkers route outbound email through Gmail, Microsoft 365, or the configured SMTP account, not through a shared Warmbly IP. Sender reputation is tied to the mailbox's own domain rather than a pool shared with every other customer on the platform. The README and architecture docs describe how workers are stateless and scale by adding more of them.
Single-command install with no external cloud dependenciesThe installer script brings up the entire platform on any Docker host without an AWS, GCP, or Stripe account. The --wizard flag steps through backup configuration, secret generation, and storage location. The --dry-run flag prints every file it would write without touching anything, and --demo walks the wizard while installing nothing.
Secrets use envelope encryptionMailbox credentials are stored with envelope encryption using an AES master key by default, or AWS KMS if preferred. Credentials never appear in the database in plaintext. The architecture documentation covers the full encryption model for operators who need to audit it before deployment.

Trade-offs

-Self-hosting requires Docker and server managementThe installer handles initial setup, but running Warmbly in production means managing backups, configuring HTTPS, rotating secrets, and handling email credentials securely. The deployment guide covers these steps, but teams without server experience will find the managed cloud plan the easier starting point. The self-hosted path also requires Docker with Compose v2 and roughly 10 GB of free disk for a source build.
-Young project with 14 open issues at time of writingWarmbly was created in January 2026 and had 14 open issues as of 2 November 2026. Some may represent known edge cases in the campaign engine or warmup pool. The issue tracker is worth reviewing before deploying into a high-volume production workflow or a time-sensitive campaign.
-Enterprise support and managed hosting pricing is not publishedWarmbly offers enterprise support and managed infrastructure for organisations that need someone else to operate the platform. Pricing and SLA terms are not listed on the website; teams that need this arrangement must contact the team directly via email or Discord to discuss scope.

versus alternatives

Warmbly vs alternatives#

Warmbly vs Instantly

Instantly and Warmbly both offer mailbox warmup and multi-step cold email sequences aimed at B2B outbound. The key decision is the licensing model and where campaign data lives.

Feature	Warmbly	Instantly
Licence	Apache-2.0	Proprietary
Self-hosted	Yes	No
Warmup pool	Yes, monitored	Yes
Unified inbox	Yes	Yes
Built-in CRM	Yes	Yes
Cloud pricing	Free tier; from $23/mo	From $37/mo

Warmbly is the better fit for teams that need data residency, want no per-mailbox fees at scale, or have a developer who can run Docker. Instantly is worth considering for teams that prefer a fully managed service with no infrastructure responsibility and run a smaller mailbox pool where per-mailbox pricing is not the deciding factor.

Warmbly vs Smartlead

Smartlead competes on warmup and multi-sender campaigns. Warmbly's key architectural difference is that outbound email leaves through each mailbox's own provider rather than a shared sending IP, which matters for teams that have built domain reputation they do not want pooled.

Feature	Warmbly	Smartlead
Licence	Apache-2.0	Proprietary
Self-hosted	Yes	No
Sending IP	Mailbox's own provider	Shared infrastructure
Cloud pricing	Free tier; from $23/mo	From $39/mo

Warmbly is the better fit for teams where sender reputation is tied to specific domains. Smartlead suits teams that want a quick managed setup and are comfortable with shared sending infrastructure.

Warmbly vs Lemlist

Lemlist specialises in personalisation features such as custom images and dynamic landing pages in email. Warmbly does not offer image personalisation; its campaign editor is text-based with variable substitution and A/B variants per step.

Feature	Warmbly	Lemlist
Licence	Apache-2.0	Proprietary
Self-hosted	Yes	No
Image personalisation	No	Yes
A/B testing per step	Yes	Yes
Built-in CRM	Yes	No
Cloud pricing	Free tier; from $23/mo	From $39/mo

Warmbly is the better choice for text-driven campaigns that need self-hosting, a built-in CRM, and no per-mailbox fees. Lemlist is the better fit when image personalisation or dynamic landing pages are central to the campaign strategy.

install · quick start

Quick start#

bash

Self-hosting Warmbly uses Docker Compose; the installer script pulls the published images and starts the stack in under two minutes.
```bash
curl -fsSL https://warmbly.com/install.sh | sh
```

tech stack · detected from GitHub

What it's built on#

Languages: ElixirGoRustSwiftTypeScript
Frameworks: Next.jsReact

frequently asked

FAQ#

Is Warmbly free to self-host?

Yes. The Apache-2.0 licence places no restrictions on self-hosting for any purpose, including commercial use. There are no mailbox limits, seat limits, or fees for running the self-hosted version. A managed cloud free tier is also available and includes ten mailboxes with no credit card required. Paid cloud plans start at $23 per month billed yearly.

How does Warmbly's mailbox warmup work?

Warmbly connects your mailboxes to a monitored pool and exchanges real email with other inboxes in the pool, starting at ten messages per day and growing gradually. The platform tracks inbox placement at Gmail, Outlook, and Yahoo. If spam placement rises on a mailbox, Warmbly automatically reduces its send volume until placement recovers. The typical ramp runs for roughly 14 days before a mailbox is ready for campaign volume, as shown in the warmup dashboard.

What email providers does Warmbly support?

Warmbly connects Google Workspace via Gmail OAuth, Microsoft 365 via Microsoft OAuth, and any standard SMTP/IMAP account. SPF and DMARC checks run automatically when you add a sending domain. There is no limit on the number of connected accounts in the self-hosted version.

Can I use Warmbly without self-hosting?

Yes. Warmbly offers a managed cloud service at warmbly.com. The free plan includes ten mailboxes and requires no credit card. Paid plans are Starter at $23 per month, Grow at $71 per month, and Business at $263 per month, all billed yearly. The Starter plan includes unlimited warmup, unlimited mailboxes, and the unified inbox. Grow adds the CRM, A/B testing, bulk contact import, and the API. Enterprise support and managed infrastructure are also available; contact the team at [email protected].

What integrations does Warmbly support?

Warmbly integrates with HubSpot, Salesforce, Pipedrive, Close, Slack, Discord, Zapier, Make, n8n, Calendly, Cal.com, and MillionVerifier. The REST API and signed webhooks, included from the Grow cloud plan and always available on self-hosted, allow custom integrations with any system that can receive HTTP events.

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Hostinger

Self-host Warmbly on a Hostinger VPS

Keep it running 24/7, even when your laptop is off. A Hostinger VPS gives it a server of its own.

01
Choose a plan
Starts from $6.49/mo
02
Apply
Extra 10% off yearly plans
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Install Warmbly
On a server that stays on
04
Start building
Focus on the app, not the server

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Find open source alternatives to paid software

Warmbly vs Instantly

Instantly and Warmbly both offer mailbox warmup and multi-step cold email sequences aimed at B2B outbound. The key decision is the licensing model and where campaign data lives.

Feature	Warmbly	Instantly
Licence	Apache-2.0	Proprietary
Self-hosted	Yes	No
Warmup pool	Yes, monitored	Yes
Unified inbox	Yes	Yes
Built-in CRM	Yes	Yes
Cloud pricing	Free tier; from $23/mo	From $37/mo

Warmbly vs Smartlead

Feature	Warmbly	Smartlead
Licence	Apache-2.0	Proprietary
Self-hosted	Yes	No
Sending IP	Mailbox's own provider	Shared infrastructure
Cloud pricing	Free tier; from $23/mo	From $39/mo

Warmbly is the better fit for teams where sender reputation is tied to specific domains. Smartlead suits teams that want a quick managed setup and are comfortable with shared sending infrastructure.

Warmbly vs Lemlist

Feature	Warmbly	Lemlist
Licence	Apache-2.0	Proprietary
Self-hosted	Yes	No
Image personalisation	No	Yes
A/B testing per step	Yes	Yes
Built-in CRM	Yes	No
Cloud pricing	Free tier; from $23/mo	From $39/mo