Open Source Alternatives to Outlook

An email and calendar service that provides cloud-based messaging, scheduling, and integration with Microsoft 365 productivity apps for individuals and organizations across devices.

Whether you want to cut software costs or escape vendor lock-in, these open source alternatives to Outlook give you an option you fully own. You can self-host them, so your data stays on infrastructure you control. This page lists 1 open source alternative to Outlook. The most popular is Roundcube Webmail. It uses the GPL-3.0 license and ships an official Docker image.