Two self-hostable engines, two very different deals underneath.
Warmbly is a genuinely open-source (Apache 2.0) cold-outreach and warmup platform you can self-host free or run on its hosted cloud. WarmHawk is source-available (Business Source License 1.1, not OSI open source) but gives every account its own single-tenant server and one flat fee with no per-volume pricing tiers. Neither is strictly “better” — they optimize for different things.
The license difference, stated plainly
Warmbly (github.com/warmbly/warmbly) is licensed Apache 2.0 — a real, OSI-approved open source license, with roughly 340 GitHub stars (GitHub API, September 2026). WarmHawk’s core engine is licensed under the Business Source License 1.1: source you can read, self-host, and modify under a non-compete grant, converting automatically to Apache 2.0 four years after each release. That is not OSI open source, and we’re not going to call it that.
If a fully open, resell-anywhere license is what you actually need — you want to fork it, redistribute it, or build a competing hosted product on top of it — Warmbly’s Apache 2.0 grant lets you do that today and WarmHawk’s BSL does not. What WarmHawk trades for that restriction is a product built specifically to run as one single-tenant install per customer, with a support and pricing model built around that same idea.
Warmup: your own mailbox pool vs your own dedicated infrastructure
Warmbly warms mailboxes by gradually ramping send volume within the pool of mailboxes you connect — “reputation-safe pools and gradual ramps that earn placement, not just inflate it,” per warmbly.com. WarmHawk runs automated per-mailbox warmup on your own dedicated, per-customer infrastructure, with no pool shared across WarmHawk customers at all.
Both approaches avoid the failure mode of a shared, vendor-wide warmup network, where one customer’s bad sending behavior can degrade IP or domain reputation for everyone sharing that pool. Warmbly’s free hosted plan includes warmup for up to 10 mailboxes with no card required; self-hosting Warmbly yourself keeps that same 10-mailbox free tier unless you pay $15/month for unlimited warmup mailboxes. WarmHawk includes warmup at no extra cost on every self-hosted account, with no separate warmup-only pricing tier.
AI compose and reply handling
Warmbly ships built-in AI compose (“ask at the caret and the draft lands where you type”) and AI-driven reply routing that classifies replies as interested, not ready, wrong person, out-of-office, unsubscribe, or bounce, feeding a unified inbox and a built-in CRM. WarmHawk instead has you bring your own Gemini or Claude API key for personalization — you pay your AI provider directly, at cost, with nothing routed through a shared gateway.
Warmbly’s AI reply triage and built-in CRM (contacts, pipelines, deals, tasks, meetings) go further than anything shipped in WarmHawk’s dashboard today — WarmHawk’s Tier 1/2 dashboard has a Unified Reply Inbox, but no pipeline/deal CRM layer on top of it. If a built-in CRM and AI-classified reply routing matter more to you than infrastructure ownership, that’s a genuine point in Warmbly’s favor. Where WarmHawk pushes back is on guardrails enforced structurally rather than left to configuration: CAN-SPAM auto-injection, RFC 8058 one-click unsubscribe on every send, CSV-injection defense, GDPR erasure, an EU AI Act disclosure marker, and a bounce/complaint circuit breaker that auto-pauses a campaign before a bad list damages a domain’s reputation.
WarmHawk vs Warmbly, side by side
Sourced from warmbly.com and github.com/warmbly/warmbly, checked September 2026.
| Warmbly | WarmHawk | |
|---|---|---|
| License | Apache 2.0 — OSI-approved open source | Business Source License 1.1 — source-available, converts to Apache 2.0 after 4 years |
| Hosting model | Self-host free, or their multi-tenant cloud from $23/mo | Self-hosted only — your own single-tenant containers, database, nginx, TLS |
| Warmup approach | Own-mailbox pool — gradual ramp within your connected mailboxes | Automated per-mailbox warmup on your own dedicated infrastructure |
| AI personalization | Built-in AI compose + reply-routing, vendor-run model | BYOK — your own Gemini or Claude key, no markup |
| Guardrails | Bounce/complaint handling, AI reply classification | CAN-SPAM auto-injection, RFC 8058 unsubscribe, GDPR erasure, bounce/complaint circuit breaker |
| Pricing | Free self-host, or hosted $23–263+/mo scaling with daily send volume | $0 API-only, or $199/mo flat — unlimited mailboxes and users |
| Support | Community (GitHub, Discord); dedicated support on Enterprise | Founder-staffed — 1 business day, 4h on critical issues |
When to pick which
- You need a genuinely OSI open-source license — Apache 2.0, no conversion wait.
- You want to try it hosted, free, before deciding whether to self-host anything.
- A built-in CRM and AI reply-routing across pipelines and deals matter to you.
- You’d rather pay less at low volume ($23/mo at 150 emails/day) than pay a flat fee upfront.
- You want true single-tenant infrastructure on every tier — your own containers, database, nginx, TLS — not a vendor-run cloud option alongside self-hosting.
- You want one flat $199/mo regardless of mailbox count, user count, or daily send volume, instead of pricing that scales with volume.
- You’d rather bring your own Gemini or Claude key and pay your provider directly than use a vendor-run AI model.
- A four-year-to-Apache-2.0 source-available license is an acceptable trade for that infrastructure model and pricing.
Questions
WarmHawk vs Warmbly: questions worth answering up front
Is Warmbly actually open source?+
Yes — genuinely so. Warmbly (github.com/warmbly/warmbly) is licensed Apache 2.0, an OSI-approved open source license, with roughly 340 GitHub stars as of September 2026. You can self-host it for free with no license restriction on running a competing service.
Is WarmHawk open source?+
No, and we’d rather say that plainly than blur it. WarmHawk’s core engine is licensed under the Business Source License 1.1 (BSL) — source-available, not OSI open source. BSL grants a non-compete license to run and modify the code, and converts to Apache 2.0 automatically four years after each release. Warmbly’s Apache-2.0 license is the more open of the two today.
Does Warmbly have a free plan, and what does it actually include?+
Warmbly’s hosted free plan covers up to 10 mailboxes and warmup, with no card and no time limit — but sending, the unified inbox, and the CRM are locked until you upgrade to a paid hosted tier starting at $23/month. Self-hosting Warmbly yourself is free under Apache 2.0 with the full feature set, including sending, with the same 10-mailbox limit on the free warmup pool (unlimited mailboxes for warmup runs $15/month self-hosted).
Which one costs less at scale?+
It depends on what scales for you. Warmbly’s hosted pricing scales with daily send volume — $23/mo for 150 emails/day up to $263/mo for 15,000/day, as of September 2026 — so a high-volume sender pays more over time. WarmHawk is flat at $199/month regardless of mailbox count, user count, or send volume once you’re past the free Tier 0 API. Self-hosting Warmbly yourself sidesteps that scaling entirely, since it’s free under Apache 2.0 either way.
Does Warmbly do the same single-tenant infrastructure WarmHawk does?+
If you self-host it, yes — you get your own Warmbly instance on your own server, same as WarmHawk. Where they differ is Warmbly also offers a hosted cloud option ("run it on our cloud or your own infra," per warmbly.com), which is presumably multi-tenant like most hosted SaaS. WarmHawk has no hosted option at all — every tier, including the free one, is self-hosted on your own server by design.
Own the infrastructure, not just the code.
Flat $199/mo, single-tenant by default, no hosted-vs-self-hosted decision to make.