What it is

Plunk is an open-source email platform written in TypeScript and released under the AGPL-3.0 license. It combines transactional email, marketing campaigns, and workflow automation in a single system, and it is positioned as a self-hosted alternative to SendGrid, Resend, and Mailgun. The project lives in the TypeScript and Node.js ecosystem, ships as a Docker image, and is documented at docs.useplunk.com with a community Discord for support.

The concrete problem Plunk solves is the cost and contact-limit structure of commercial email providers. The project advertises $0.001 per email with no contact limits, and it is free to self-host, so teams that send transactional messages and newsletters can run the sending infrastructure themselves instead of paying per-contact or per-volume pricing. It also removes the need to stitch together separate tools for transactional sends, campaigns, and automation, because all three share one contact list, one segment model, and one analytics view.

Key capabilities

• Transactional email sent directly from an API, with template support and variable substitution.
• SMTP relay mode, so Plunk can send mail on behalf of any existing tool or framework.
• Campaigns for newsletters and product updates aimed at large audiences.
• Workflows with triggers, delays, and conditional logic for advanced automation.
• Segments built from dynamic filtering to target specific audiences.
• Contact management with custom fields and full activity history.
• Analytics covering opens, clicks, bounces, and engagement metrics in real time.
• Custom domains verified with DKIM and SPF support, plus inbound email processing with custom routing rules.

Who uses it and how

• Product teams send transactional mail such as receipts and notifications from their application API.
• Teams already running another framework point that framework at Plunk as an SMTP relay rather than rewriting send logic.
• Marketing groups run newsletters and product updates as campaigns against a segmented contact list.
• Growth and lifecycle teams build automated sequences using workflow triggers, delays, and conditional branches.
• Operators configure inbound routing rules to receive and process incoming mail, and verify their own domains with DKIM and SPF before sending.

Getting started

The README states that the easiest way to self-host is the plunk Docker image, pulled from the GitHub container registry, with a full deployment guide in the documentation at docs.useplunk.com/self-hosting/introduction.

When to use it — and when not to

Plunk is a reasonable fit when the goal is to replace SendGrid, Resend, or Mailgun pricing with a self-hosted system that has no contact limits and a flat per-email cost. A self-hoster must operate the deployment themselves, including the Docker image and the domain verification work for DKIM and SP