Open Source Go Email Software

Performance and features packed into a single binary. Manage millions of subscribers across many single and double opt-in lists with custom JSON attributes for each subscriber. Query and segment subscribers with SQL expressions. Use the super fast bulk importer (10k records per second) or use HTTP/JSON APIs or interact with the simple table schema to integrate external CRMs and subscriber databases. Visualize and compare campaign performance. Connect external visualization programs to the database easily with the simple table structure. Create powerful, dynamic e-mail templates with the Go templating language. Use template expressions, logic, and 100+ functions in subject lines and content. Write HTML e-mails in a WYSIWYG editor, Markdown, raw syntax-highlighted HTML, or just plain text. Highly configurable, multi-threaded, high-throughput multi-SMTP e-mail queues for super fast campaign delivery.

Inspired by MailCatcher, easier to install. Built with Go, MailHog runs without installation on multiple platforms. Run it from Docker Hub or using the provided Dockerfile. The SMTP server starts on port 1025, the HTTP server starts on port 8025, in-memory message storage. ESMTP server implementing RFC5321. Support for SMTP AUTH (RFC4954) and PIPELINING (RFC2920). Web interface to view messages (plain text, HTML or source). Supports RFC2047 encoded headers. Real-time updates using EventSource. Release messages to real SMTP servers. Chaos Monkey for failure testing. HTTP API to list, retrieve and delete messages. See APIv1 and APIv2 documentation for more information. HTTP basic authentication for MailHog UI and API. Multipart MIME support. Download individual MIME parts. In-memory message storage. MongoDB and file based storage for message persistence. Lightweight and portable. No installation required.

Proton Mail Bridge is a desktop application that runs in the background on Windows, macOS, and Linux to enable users to access their Proton Mail encrypted email accounts with traditional email clients like Outlook, Thunderbird, Apple Mail, and others via local IMAP/SMTP servers. Because standard IMAP cannot natively decrypt end-to-end encrypted messages, Bridge acts as a translator that downloads encrypted mail, decrypts it locally, and serves it to your preferred mail client over a local server, while encrypting outgoing messages before they’re sent to Proton’s servers. It provides a seamless integration layer for users who need offline support, familiar local client workflows, or tighter integration with desktop tools while preserving Proton’s zero-access encryption model. The Bridge app continues running even when its GUI is closed so that mail clients can remain connected and synchronized, and it supports automatic startup and robust credential handling via secure storage.

peco (pronounced peh-koh) is based on a python tool, percol. percol was darn useful, but I wanted a tool that was a single binary, and forget about python. peco is written in Go, and therefore you can just grab the binary releases and drop it in your $PATH. peco can be a great tool to filter stuff like logs, process stats, find files, because unlike grep, you can type as you think and look through the current results. Demos speak more than a thousand words! Here's me looking for a process on my mac. You can page through your results, and you can keep changing the query. When you combine tools like zsh, peco, and ghq, you can make managing/moving around your huge dev area a piece of cake! Search results are filtered as you type. When you find that line that you want, press enter, and the resulting line is printed to stdout, which allows you to pipe it to other tools. You can select multiple lines!

MOSINT is the fastest OSINT Tool for emails. It helps you gather information about the target email. Email validation, check social accounts, check data breaches and password leaks, finding related emails and domains, scan Pastebin Dumps. Google Search and DNS Lookup.

msgvault is a message archiving tool for email and chat history, built for offline search, analytics, and AI-assisted querying. It lets users preserve large volumes of personal or organizational messages in a local archive. The project uses DuckDB to support fast aggregate queries across hundreds of thousands of messages. It includes a terminal interface, command-line tools, and an MCP server for connecting archived messages to AI assistants. Users can search, analyze, and read their message history conversationally through compatible AI clients. It also supports scheduled syncs, remote server mode, multi-account setups, and configuration options for personal Gmail or Google Workspace environments.

Notifuse is an open-source, modern, self-hosted emailing and communications platform designed to replace proprietary services like Mailchimp, Brevo, and Klaviyo with a self-managed solution. It’s built with a Go backend and a React frontend to offer both developer-friendly APIs and a user-centric visual interface with enterprise-grade capabilities such as campaign creation, subscriber segmentation, and detailed analytics. Notifuse supports both newsletters and transactional emails through a RESTful API, letting organizations maintain full control over their email infrastructure without expensive per-message pricing. The system includes a drag-and-drop MJML email builder, webhook integrations, and multi-provider support for SMTP services and cloud providers, while also tracking opens, clicks, and delivery performance in real time.