Open Source Alternatives to Microsoft Outlook

Switching from Outlook to an open source alternative removes the requirement to hold a Microsoft 365 subscription just to access a mail client, since standards-based clients connect to any IMAP or CalDAV-compliant mail and calendar server rather than only Exchange. Open source email clients also add built-in encryption options like OpenPGP that aren’t native to Outlook. For most personal and small-business email, calendaring, and contact management, this alternative covers Outlook’s core capabilities at no cost, though organizations with deep Exchange/Microsoft 365 integration needs may still prefer Outlook’s native connectivity.