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Plunk

The open-source email platform·useplunk.com

Plunk is an open-source email platform for developers that unifies transactional email, marketing campaigns, and workflow automation against a single contact list, triggered from one API. It supports a REST API, an official Node SDK, and SMTP, and can be used as a hosted service or self-hosted via Docker under an AGPL-3.0 licence. It also offers inbound email handling, dynamic segmentation, campaign analytics, and an MCP server that lets AI agents like Claude or Cursor manage email.

What it's for

Sending transactional emails (signup confirmations, password resets, receipts)Running marketing campaigns and newsletters/broadcasts to a segment or full listBuilding event-triggered automated email workflows with delays and branchingReceiving inbound email at a verified domain and turning replies into events/contactsDynamic audience segmentation based on contact data and behaviorUsing an AI agent (via MCP) to draft, segment, and send campaigns

Features 14

Campaign broadcasts to full list or targeted segments
Click and open tracking, bounce and unsubscribe analytics
Custom domains with automatic DKIM, SPF, and DMARC setup
Dynamic audience segmentation based on behavior and attributes
Event-triggered workflow automation with delays, conditions, and branching
Full REST API with SDKs (Node.js, Python)
Inbound email receiving that turns replies into contacts/events
MCP server with 23 tools for AI agents (read-only mode available)
Open-source, inspectable and forkable codebase (AGPL-3.0)
Self-hosting via Docker Compose
Transactional email sending via API and SMTP
Unified contact timeline across transactional, campaign, workflow, and inbound events
Unlimited contact storage
Visual and code-based email editor

At a glance

free tieropen sourceself-hostableAPI

TypeWeb app

DeploymentHybrid

PlatformsWeb

Fordevelopers

CompanyPlunk

Integrations

ClaudeCursor

Complianceself-reported

GDPR

Resources

Docs

Pricing

Paid plan bills $0.001 per email with a monthly spend cap and no feature tiers. The site compares this to other providers at 10,000 emails/month: SendGrid $0.002/email, Mailgun $0.003/email, Mailchimp $0.004/email (per equivalent plans).

Free foreverFree

Transactional emails, Workflow automation, Campaign broadcasts, Custom domains, Click & open tracking, Unlimited contacts, Plunk branding on emails

1,000 emails per month, no credit card required

Pay as you growQuote

Everything in Free, No Plunk branding, Monthly spend cap, Unlimited emails

Monthly spend cap; unlimited emails and unlimited contacts