The largest open-source cold email platform.
Warmbly markets an open-source, self-hostable cold-email platform that warms mailboxes, sends campaigns, and triages replies; its hosted cloud product is described as coming soon.
| Plan | Price | Included | Notable |
|---|---|---|---|
| Starter | $23/mo billed annually | 150 emails/day | Unlimited mailboxes, Unlimited warmup, Unified inbox |
| Grow | $71/mo billed annually | 3,000 emails/day | CRM, pipelines, deals, and tasks, API and HMAC-signed webhooks, Custom tracking domain |
| Business | $263/mo billed annually | 15,000 emails/day | Dedicated IPs, Team roles and audit log, Priority support |
| Enterprise | Custom volume-based · contact sales | 15,000+ emails/day | SSO/SAML and SCIM, Custom contract, Dedicated CSM and SLA |
Checked 2026-08-08 against their pricing page. Vendors change pricing without notice.
Warmbly is a cold-email and mailbox-warmup product. The retrieved documentation explains how to connect Gmail, Microsoft 365, or IMAP/SMTP sender accounts; the product site says the software is Apache-2.0 licensed and self-hostable.
Outbound teams that operate multiple sending mailboxes and want branching sequences, warmup, a shared inbox, and the option to self-host.
Teams that cannot accept the operational responsibility of self-hosting, or that need a mature hosted service immediately, should look elsewhere: Warmbly says its cloud is coming soon, and its self-hosted route means owning the deployment.
No curated rival set covers this tool yet, so these are simply other tools in the same architectural layer and product form. Treat it as a starting point, not a shortlist.
Yes. The product site says it is Apache-2.0 licensed and can be self-hosted.
The mailbox documentation covers Gmail/Google Workspace with OAuth, Outlook/Microsoft 365 with OAuth, and other servers through IMAP and SMTP.
The docs say the OAuth routes return a token instead of a password; the provider-native APIs are used for those connections.
Starter is listed at $23/month billed annually, with unlimited mailboxes and warmup plus 150 emails/day.
The integrations page describes OAuth connections for CRMs and a signed webhook stream; Grow includes API and HMAC-signed webhooks.
This page tells you whether Warmbly fits. Cheetah builds and runs the system it goes into — enrichment, sequencing, CRM and the joins between them.
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