Go-mapi

Windows has a built-in email functionality called MAPI (Messaging Application Programming Interface) that allows any program to send emails through the default email client. This powers features like Send to → Mail recipient in Windows Explorer, Email buttons in PDF readers and Office applications, and Print to PDF and email workflows. Gmail and Google Workspace have never been compatible with MAPI. If Gmail is your email provider, these features simply don't work. go-mapi is the open-source bridge that fixes this gap.

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• MAPI call interception (DLL). A DLL file written in C++ that injects itself into Windows application processes (like explorer.exe). It intercepts the MAPISendMail function, converts the data (recipients, subject, body, attachments) to JSON format, and writes this file to a specific temporary folder (%TEMP%\go-mapi\). It acts as the gateway that captures the email request from the program.
• File watcher (Native Go host). A binary executable written in Go that runs in the background. Its main function is to constantly monitor the %TEMP%\go-mapi\ folder for new JSON files created by the DLL interceptor. When it detects one, it reads it and acts as a bridge, sending the email information to the browser extension via the Chrome/Edge native messaging protocol.
• User interface and sending (Browser extension). An extension for Chrome and Microsoft Edge developed with React and TypeScript. It provides a popup window displaying the captured email. It allows the user to edit the content, save the message as a draft in Gmail, or send it immediately. It uses the Gmail API and the browser's OAuth identity system for secure authentication with the Google account.
• Automatic installer (PowerShell). A PowerShell script that automates the entire installation process. It downloads the latest version of the binaries from GitHub, installs them to C:\Program Files\go-mapi\, registers go-mapi as the default MAPI client in the Windows registry, and configures native messaging for the browser extension, automatically detecting the installed extension's ID.
• Complete logging and uninstallation. The installer includes an uninstall function that removes all entries from the Windows registry, restores the previous email client, and can optionally keep or remove program files, ensuring a clean system rollback.
• UTF-8 and attachment support. The system correctly handles international character encoding (UTF-8) in message bodies and file names. Attachments are processed and sent using the Gmail API, respecting this service's size limits.
• Unattended installation mode. The installation script has an -Unattended parameter that allows installation without manual intervention, showing progress messages but requiring no confirmations. It is ideal for automated deployments via configuration management tools like SCCM or Intune.
• Specific version and local installation. Advanced installer functionality to pin a specific version of the binaries using the -Version parameter, or to perform an installation from a local build directory using the -Local parameter, facilitating development and testing.
• Draft creation in Gmail. The extension offers the option to save the captured email as a draft in Gmail. This allows the user to review and edit the message in the Gmail web interface before final sending.
• Desktop notifications. The system can generate alerts on the Windows desktop to notify the user when a new email has been processed and is ready to be viewed in the browser extension.
• Multi-process and 32/64-bit application support. The DLL interceptor is designed to work correctly with both 32-bit and 64-bit applications, and handles concurrency when multiple applications try to send emails simultaneously.
• Automatic extension detection. The installation script examines Chrome and Edge browser profiles to automatically locate the unique identifier of the installed go-mapi extension, saving the user from having to copy and paste it manually.

The development of go-mapi was initiated by Marc Fargas to offer an open-source alternative following the announcement of the shutdown of Affixa, a commercial tool that provided similar functionality. The project began in February 2026, quickly reaching its stable version 1.0.0. It is written in multiple languages: C++ for the DLL interceptor, Go for the native messaging host, and TypeScript with React for the browser extension.

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