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Warmbly is an open-source platform that warms mailboxes, sends campaigns, and triages replies.
Grounded in available product and source data
Most cold-email tools stop at sending a sequence — Warmbly is open-source cold email and inbox warmup built to cover what happens before and after that too, warming a mailbox's reputation first and triaging every reply once campaigns are live.
Warmup itself is framed around earning placement rather than just running volume: reputation-safe pools and gradual sending ramps aim to build a mailbox's sender reputation before it's used for real outreach, rather than treating warmup as a numbers game. Campaigns then build on a visual canvas where sequences branch on real recipient behavior — opened, clicked, replied — with weighted A/B variants and threaded follow-ups that stay in the same email conversation instead of starting a new one each time.
Once replies start coming in, Unified Inbox streams every reply, bounce, and out-of-office message across every connected mailbox into one queue, automatically classified on arrival, and Automations can act on that classification directly — opening a CRM deal, posting to Slack, or calling a webhook the moment a reply is flagged positive, with a dry-run test mode to check the logic before it fires on real messages. A built-in CRM keeps that same positive-reply handoff native to the platform, pausing the sequence and opening a deal automatically rather than requiring a separate tool to catch the handoff.
For teams that want to build on top rather than just use the dashboard, a Developer API exposes the whole platform as REST endpoints with scoped keys, idempotent writes, and HMAC-signed webhooks, and integrations connect over OAuth to Gmail, Microsoft 365, Slack, HubSpot, and Salesforce, with the site stating OAuth tokens are encrypted at rest.
Warmbly is genuinely open-source under Apache 2.0, self-hostable end to end, or runnable on Warmbly's own cloud with a 14-day trial covering 3 mailboxes and no credit card required.
It can be self-hosted entirely — the platform is genuinely open-source under Apache 2.0 with the source on GitHub, so a team can run it on its own infrastructure instead of Warmbly's cloud.
No, that's handled automatically — a reply classified as positive opens a deal in the built-in CRM and pauses the sequence on its own, without a separate integration step to catch the handoff.
Yes — a dry-run mode fires the automation against a sample event and shows the verdict at every node, so the logic can be checked before it's switched on for real incoming messages.
It exposes a full Developer API — every dashboard feature is available as a REST endpoint with scoped keys and HMAC-signed webhooks, so custom tooling can be built rather than being limited to the built-in UI.
The site states OAuth tokens are encrypted at rest and every webhook is HMAC-signed with SSRF protection, so a connected mailbox's credentials aren't stored or transmitted in plaintext.
There's a companion iOS app built in the same open-source repo, running on the same realtime connection as the web dashboard, for triaging replies and checking mailbox health from a phone — the page reviewed doesn't mention an Android equivalent.
