Plunk

Plunk puts transactional email, marketing campaigns and workflow automation in one self-hosted platform, so a product team stops paying for and stitching together a separate sender, newsletter tool and automation service. It positions itself against SendGrid, Resend and Mailgun.

Mail leaves through the API with template support and variable substitution, or through Plunk acting as an SMTP relay, which lets any existing tool or framework send through it without code changes.

Beyond sending, the platform manages the audience and the reporting.

• Campaigns: send newsletters and product updates to large audiences.
• Workflows: build automations with triggers, delays and conditional logic.
• Segments: filter contacts dynamically to reach the right audience.
• Contact management: keep custom fields and a full activity history per contact.
• Analytics: track opens, clicks, bounces and engagement in real time.
• Inbound email: receive incoming messages and route them with custom rules.

Custom domains are verified with DKIM and SPF so mail goes out under your own name. The easiest deployment is the official Docker image, with a full guide in the documentation, and the code is licensed AGPL-3.0. The project advertises a cost of $0.001 per email and no contact limits, which suits teams mailing long lists.