Warmbly

Warmbly is an open-source outreach platform for teams that want warmup, campaigns and contact management together. It is best suited to founders, agencies and sales teams running multi-mailbox campaigns; the main trade-off is a 100-per-day cold-send cap per mailbox on its three named paid plans.

Overview

Warmbly brings email warmup, campaign sending, inbox handling, analytics and CRM into one system. That breadth can reduce the need to stitch together separate tools for outreach and reply management, while Apache 2.0 licensing offers a self-hosted route at no software cost. When self-hosted campaigns are linked to Warmbly Cloud for warmup, campaigns, contacts and inbox data remain on the self-hosted server.

Warmbly says mailbox credentials and message bodies are encrypted at rest, and uses TLS 1.2 or above in transit alongside AWS KMS-backed, per-organization AES-256-GCM application-layer encryption. Its data handling is described as GDPR-aligned; SOC 2 Type II and ISO 27001 are planned, not claimed certifications.

Key features

Campaigns and timing

Sequences can branch on opens, clicks and replies, use A/B variants, and keep follow-ups in the same conversation thread. This suits teams that want outreach to respond to engagement rather than run as a fixed chain. Weekday sending windows can be configured for a selected timezone, helping keep campaigns within a chosen working day.

Inbox, integrations and API

The unified inbox classifies replies, bounces, out-of-office messages and clicks across connected mailboxes, giving teams a single place to triage campaign activity. Integrations include HubSpot, Salesforce, Pipedrive, Close, Zapier, Make, n8n, Slack, Discord, Calendly and Cal.com; Google Sheets lead sync is available on demand. For teams building their own connections, webhooks cover 21 event types, use HMAC-SHA256 signatures, and support event filters and secret rotation.

Self-hosting and scale

Self-hosting is free and keeps campaigns, contacts and inbox data on the server when Warmbly Cloud is linked for warmup. This is a meaningful option for teams prioritizing control over those records, but it does not remove the sending limits of the named paid plans: Starter, Grow and Business each cap cold sends at 100 per day per mailbox. Enterprise uses a custom cap.

Pricing

Warmbly has two warmup-pool options as well as paid outreach plans. The free pool warms up to 10 mailboxes, making it a narrow fit for small setups that need warmup but not the full paid workflow. The Unlimited warmup-pool tier costs $15 a month and allows unlimited mailboxes, with paid-tier partners first.

Starter costs $23 a month, billed annually with 20% off. It includes unlimited mailboxes and warmup, 150 emails per day, a unified inbox with reply detection, and branching sequences. It is the entry point for teams that need campaign workflows as well as warmup, but the daily cold-send cap is 100 per mailbox despite the plan's 150-emails-per-day allowance.

Grow costs $71 a month, billed annually with 20% off. It adds CRM tools for pipelines, deals and tasks, API access, HMAC-signed webhooks and a custom tracking domain, while retaining unlimited mailboxes and warmup. It suits teams that need the CRM and integration layer; it does not raise the 100-per-day cold-send cap per mailbox.

Business costs $263 a month, billed annually with 20% off. It includes 15,000 emails per day, sending kept apart from other customers, team roles, an audit log and priority support, alongside unlimited mailboxes and warmup. It fits larger teams needing separation and administration, though the per-mailbox cold-send cap remains 100 per day.

Enterprise has custom, volume-based pricing and includes 15,000+ emails per day, SSO/SAML, SCIM, a custom contract, a dedicated customer success manager and an SLA. It is the option for organizations needing those controls and a negotiated volume cap. Starter includes community support, Grow email support, Business priority support and Enterprise dedicated support. Payment card data is held by Stripe rather than Warmbly's servers.

Platforms

Warmbly is available on the web, through an API, and as self-hosted software. Self-hosting is particularly relevant for teams that want campaign records to remain on their own server while using Warmbly Cloud for warmup.

Who it's for

Warmbly identifies founders, agencies, sales teams, recruiters and fundraisers as intended users. It is a strong fit for those groups when one platform for warmup, branching outreach, reply classification and CRM is more useful than a narrow warmup tool. Smaller teams can start with the free warmup pool; teams needing CRM, webhooks or higher campaign allowances will need a paid plan. The low daily cold-send ceiling per mailbox makes it a weaker fit for high-volume outreach.

Pros and cons

• Pros: Branching sequences, A/B variants and threaded follow-ups support responsive campaign workflows.
• Pros: Self-hosting is free, and linked warmup does not move campaigns, contacts or inbox data off the self-hosted server.
• Pros: A unified inbox, CRM options and integrations cover multiple parts of the outreach process.
• Cons: Starter, Grow and Business all cap cold sending at 100 per day per mailbox, limiting throughput even as plan-level email allowances rise.
• Cons: Starter has community support, so teams wanting direct email help must move to Grow or above.
• Cons: The free warmup pool is capped at 10 mailboxes; unlimited warmup requires a paid pool or outreach plan.

Alternatives

For a broader comparison, see Cold Email Software.

• Mixmax is worth considering for a freemium tool with a free trial and tracked-email and sequence-recipient quotas on its free plan.
• Yesware offers a free plan and trial, with basic open and attachment tracking, a 10-recipient campaign limit and meeting scheduling.
• Regie.ai has a free plan with 250 one-time, non-expiring credits per person for research, enrichment, drafting and agents.
• Growbots may suit teams looking for a free outreach plan with 20 email accounts, three sequences and partial access to a 180M+ prospect database.
• Mails.ai offers a free plan with 3,000 events per month, one agent and TypeScript and Python SDKs, REST and MCP access.
• Mystrika is another freemium option.
• Outplay offers a free plan for one user, two mailboxes and 2,000 active prospects per month, plus a free trial.
• ReachInbox is a freemium alternative with a paid Starter plan that includes unlimited email accounts and warmup, plus monthly active-lead and email quotas.

Verdict

Choose Warmbly if your team wants warmup and a substantial outreach workflow in one open-source product, especially if self-hosting campaign data matters. Its branching sequences, inbox classification and optional CRM make it more than a warmup utility. Look elsewhere if your priority is high daily cold-send volume per mailbox: the 100-per-day cap on the three named paid plans is the clearest constraint.