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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MS workload name
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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Existing add-ins may fail to retrieve inline images due to outdated parsing logic, leading to broken image displays in emails.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**
Starting November 15, 2025, there will be a change in how Outlook on the web and the new Outlook for Windows handle inline images in emails. Imagine you are used to receiving letters with photos attached. Previously, these photos came with a little note that said, "This photo is attached with ID number 123." You could use this ID to easily find and view the photo. However, now, instead of using these ID numbers, the photos will come with a special stamp, like a unique watermark, that helps identify them. This new method is more secure and helps protect the photos from being accessed improperly.
For those who create add-ins for Outlook, this means they need to adjust how they recognize and handle these photos. Instead of looking for the ID number, they will now look for this special stamp. They will use new tools provided by Microsoft to match the stamp with the photo and ensure everything works smoothly.
This change is similar to switching from using a password to using a fingerprint to unlock your phone. It's a more secure way to ensure that only the right people can access the information. Developers need to update their tools to recognize this new method, much like updating a phone to read fingerprints instead of passwords.
Overall, this update is about enhancing security and ensuring that inline images in emails are handled in a more secure manner. Developers and support teams will need to adapt to this change to continue providing a seamless experience for users.
** AI generated content. This information must be reviewed before use.
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