check before: 2025-11-15
Product:
Entra, Microsoft 365 Apps, Microsoft 365 for the web, Outlook, Windows
Platform:
Developer, Online, Web, World tenant
Status:
Change type:
User impact, Admin impact
Links:
Details:
Summary:
Starting November 15, 2025, Outlook on the web and new Outlook for Windows will update inline image handling by replacing tokenized URLs with content IDs (cid) in the HTML. Add-ins must update parsing logic to use content IDs and new APIs to correlate and retrieve inline images securely.
Details:
[Introduction]
Starting November 15, 2025, Outlook on the web and the new Outlook for Windows will begin rolling out an update to how inline images are represented in the HTML body of emails. This change is part of Microsoft's ongoing security improvements and will affect how Outlook add-ins identify and process inline images using the attachment ID. Specifically, the update transitions from using tokenized image URLs to a more secure method using content IDs and request headers.
[When this will happen:]
This change will begin rolling out on November 15, 2025, to Production users. Rollouts to other environments will begin after Production rollouts are 100% complete.
Change Category:
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Scope:
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Release Phase:
Created:
2025-10-18
updated:
2025-10-18
Task Type
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Docu to Check
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MS How does it affect me
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MS Preperations
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MS Urgency
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summary for non-techies**
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Direct effects for Operations**
Add-in Functionality
Existing add-ins may fail to retrieve inline images due to outdated parsing logic, leading to broken image displays in emails.
- roles: Developers, Support Teams
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
User Experience
Users may experience a lack of inline images in emails, resulting in confusion and decreased productivity.
- roles: End Users, Helpdesk Staff
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Compliance Issues
Changes in how inline images are accessed may lead to compliance risks if add-ins do not handle personal data correctly.
- roles: Compliance Officers, Developers
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Documentation Updates
Internal documentation may become outdated, leading to confusion among developers and support teams regarding the new image handling method.
- roles: Developers, Technical Writers
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Testing and Validation
Inadequate testing of add-ins with the new image handling may result in undetected issues, affecting user trust and satisfaction.
- roles: Quality Assurance, Developers
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Configutation Options**
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Opportunities**
Enhancing Add-in Development Efficiency
With the transition to content IDs for inline images, developers will need to update their parsing logic. This presents an opportunity to streamline add-in development processes by implementing automated testing frameworks that ensure compliance with both old and new methods. This can improve the reliability and speed of updates, as well as reduce the potential for errors during the transition.
- next-steps: Identify current add-in development practices, evaluate existing testing frameworks, and integrate automated testing solutions to accommodate the new parsing logic for inline images.
- roles: Developers, Product Managers, IT Administrators
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Improving User Support Documentation
The update necessitates changes in how support teams assist users with Outlook add-ins. By creating comprehensive internal documentation that reflects the new image handling methods, organizations can improve user experience and reduce the volume of support tickets related to this change.
- next-steps: Draft updated documentation that outlines the new processes for handling inline images in Outlook add-ins, and train support staff on these changes to ensure they can effectively assist users.
- roles: Helpdesk Support, IT Administrators, Training Coordinators
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Security Compliance Enhancements
The shift to using content IDs and secure headers for inline images enhances data security and compliance with privacy regulations. This presents an opportunity to conduct a security audit of all Outlook add-ins to ensure they are compliant with the new standards and to implement best practices for data handling.
- next-steps: Schedule a security audit of existing add-ins, focusing on how they handle inline images and other sensitive data, and develop a plan to address any compliance gaps identified during the audit.
- roles: Compliance Officers, IT Security Teams, Developers
- references: https://devblogs.microsoft.com/microsoft365dev/changes-to-inline-images-in-outlook/
Potentional Risks**
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IT Security**
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explanation for non-techies**
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** AI generated content. This information must be reviewed before use.
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