Microsoft has officially announced the end of support for Office Online Server, effective December 31, 2026. This decision affects organizations that rely on on-premises browser-based document editing and viewing capabilities, pushing them toward Microsoft 365 or alternative solutions as they plan their migration strategies.
What is Office Online Server
Office Online Server was designed to provide browser-based versions of Word, Excel, PowerPoint, and OneNote for on-premises environments, enabling organizations to maintain control over their infrastructure while offering web-based document collaboration. It works with products and services that support WOPI (Web Application Open Platform Interface protocol), including SharePoint Server and Exchange Server, enabling users to view and edit Office documents through supported web browsers on computers and mobile devices without requiring Office installations on local machines.
Understanding the Retirement
Microsoft decided to retire Office Online Server to focus its browser-based Office investments on cloud-first solutions through Microsoft 365, modernizing productivity experiences as organizations have increasingly adopted cloud services rather than maintaining on-premises infrastructure.
After December 31, 2026, the platform will no longer receive security updates, bug fixes, or technical support from Microsoft, potentially exposing systems to security threats and compliance risks.
Importantly, this retirement does not impact products that integrate with Office Online Server, including Exchange Server Subscription Edition, SharePoint Server Subscription Edition, and Skype for Business Server Subscription Edition, which will continue to receive support. However, organizations using Office Online Server for attachment previewing in Outlook Web Access (OWA) will need to find alternative solutions.
Migration Challenges
Transitioning from Office Online Server to Microsoft 365 presents several challenges for organizations with established on-premises infrastructure. Migration complexity increases for organizations managing hybrid environments that blend on-premises and cloud resources, particularly those with regulatory requirements mandating data remain within specific geographic boundaries.
Security concerns about data exposure during transit remain a primary consideration, though Microsoft has implemented multiple safeguards to protect information throughout the migration process. Organizations must also address DNS configuration requirements, potential throttling issues, and the transition of linked resources like Excel spreadsheets embedded in SharePoint.
For organizations using Office Online Server with Power BI Report Server to host Excel workbooks, Microsoft notes that this functionality will no longer be supported, recommending migration to the Power BI service or viewing workbooks through the Excel desktop application.
Preparing for the Transition
Microsoft recommends organizations begin planning their transition immediately to avoid security, compliance, and productivity risks after the December 2026 deadline. Organizations with 150 or more licenses can engage Microsoft FastTrack for migration planning and support. For SharePoint Server Subscription Edition and Exchange Server Subscription Edition environments, Microsoft 365 Apps for Enterprise and Office LTSC 2024 remain supported desktop clients for viewing and editing documents hosted on those servers.
Hybrid deployment models may offer a middle ground for organizations that need to maintain control over sensitive data while benefiting from cloud-based collaboration capabilities. These configurations allow businesses to retain on-premises mailboxes and data stores while gradually integrating Microsoft 365 services.
Secure Attachment Viewing for Exchange Environments
For organizations running Exchange Server environments—particularly those maintaining on-premises deployments for compliance or security reasons—finding a secure replacement for Office Online Server’s attachment viewing capabilities is critical. Messageware AttachView provides a proven solution that addresses this need while enhancing security posture.
AttachView converts over 400 types of email attachments into secure HTML pages directly within Outlook Web Access, eliminating the need to transfer files to local computers. This approach prevents data exposure that can occur when users download and open attachments on potentially unmanaged devices. Exchange administrators gain granular control over users’ ability to open, view, save, copy, and print attachments based on users, groups, IP addresses, and corporate devices—essential for organizations with strict compliance requirements.
As you evaluate your options following Office Online Server’s retirement, consider how AttachView can provide secure, fast attachment conversion while maintaining the control and data sovereignty. Learn more about how Messageware AttachView can enhance your Exchange environment’s security at https://www.messageware.com/attachview.
Fortify Your Server with Messageware Security
Data breaches have increased by 72%, servers are compromised in under 90 minutes. Ensure you have multiple layers of security software protecting your Windows Servers.
Z-Day Guard for All Windows Servers: Next-gen server protection, providing detection, alerting, and response (MDR) to zero-day and server penetration cyber-attacks. Leverages embedded monitoring technology that cannot be turned off by malicious software. No need to research complicated deployments and no learning curve to install and manage.
EPG Guard for Exchange Servers: Real-time security. Stop AD account lockouts, eliminate password attacks, intelligent GEO blocking, and prevent Exchange Server vulnerability probing.
Don’t leave your critical infrastructure vulnerable, be proactive and stay ahead of evolving threats.