Olib AI
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Open Source Mail

MailCue

Realistic email testing server in a single Docker container

MailCue is a complete, self-contained email testing server packaged in a single Docker container. It provides full SMTP, IMAP, and POP3 servers, DKIM, DMARC, and SPF authentication verification, SpamAssassin spam filtering, a REST API with Python and Node.js SDKs, an interactive web UI, and a Model Context Protocol (MCP) server for AI agents. MailCue allows engineering teams to verify transactional email workflows, header signing, and spam scores locally without sending messages to real inboxes.

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Deployment SpecHardware First
DistributionDocker container image on GitHub Container Registry
Protocols SupportedSMTP, IMAP, POP3, HTTP REST API, MCP
Deliverability ToolsDKIM, SPF, DMARC validator, SpamAssassin analyzer
SDKsPython and Node.js official client libraries
Zero Telemetry Standard:No marketing trackers, no remote analytics telemetry, and complete data ownership.
1 Container
Single Docker Image
Everything needed for mail testing running in one light container.
5 Protocols
Auth Verification
Tests SMTP, IMAP, POP3, DKIM, DMARC, and SPF verification out of the box.
REST + MCP
Agent Integrations
Python/Node SDKs and a built-in MCP server for AI coding agents.
MIT
Open Source
Free and open source for commercial workflows and CI pipelines.
Specifications verified from source build
Mail Server01

Full Protocol Stack

Runs real SMTP, IMAP, and POP3 endpoints. Your applications send and fetch mail using standard mail clients and libraries.

Deliverability02

Authentication & Spam Scoring

Verifies cryptographic DKIM signatures, evaluates SPF and DMARC alignment, and runs SpamAssassin checks on every message.

Agent Testing03

AI Agent MCP Server

Exposes tools over MCP so AI agents running tests can inspect received emails, click verification links, and assert header values.

Developer UI04

Modern Web Inspection UI

Inspects raw MIME headers, HTML and plain-text renderings, attachment payloads, and deliverability verdicts in real time.

Core Engineering Capabilities

Detailed feature checklist for MailCue, designed and audited for stability in real operational environments.

Single Docker container running SMTP, IMAP, POP3, and web dashboard

Built-in verification for DKIM signatures, SPF records, and DMARC policies

Automated SpamAssassin spam rating analysis on every received message

Native MCP server enabling AI coding agents to verify emails in automated tests

Python and TypeScript client SDKs for straightforward test assertions

Completely free and open source under the MIT License

Part of the Olib AI Ecosystem

Every product we ship serves as concrete proof of the systems and architectures we build for clients.

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Custom Engineering

Need MailCue customized for your enterprise?

Every capability in our products can be tailored and deployed inside your private infrastructure. You own the code, the models, and the data.

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