Microsoft Office 365 Version 26.03.19725.20152 breaks Exchange SE add-ins

Hi Robert Loglisci

Thank you for reaching out to the Microsoft Q&A Forum and for sharing your findings.

I really appreciate the time and effort you’ve taken to test and identify the behavior across different Office versions. 

I’ve checked available information, and at the moment I haven’t found any official confirmation or known issue matching what you described. However, based on your testing, this may be related to that specific Office version. 

As a temporary workaround, you may continue using the stable version (such as 26.02) and try updating again once a newer build becomes available. 

May I know if you have an active Microsoft 365 subscription and access to the Admin Center? If so, you can raise a support ticket directly from there with the Microsoft Support team so the issue can be looked into further.

For further instructions, you can follow this guide: Get support - Microsoft 365 admin | Microsoft Learn.      

Please note that this is a public peer-to-peer community forum. While moderators and community members can share guidance and experiences, we do not have access to internal systems and are not able to directly escalate issues to the product team.

Thank you for your understanding. 

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The described behavior matches a class of known Outlook/Office add-in regressions introduced by specific Microsoft 365 Apps builds, where changes in authentication or add-in plumbing temporarily break Exchange-based add-ins (including third‑party solutions like Zoom and security/phishing add-ins).

From the available information, there is no documented, customer-side permanent fix for a specific build such as 26.03.19725.20152 beyond:

1. Reverting to a prior working build.
2. Updating to a newer build that contains a fix or mitigation.

The pattern documented for other add-in regressions is:

1. A specific build introduces an authentication or add-in loading regression (often related to Exchange Web Services (EWS) or REST changes) that causes add-ins to fail to load, appear missing, or misbehave.
2. Microsoft rolls out a mitigation or fix in a subsequent build; customers either:
   • Wait for the fixed build to reach their update channel, or
   • Manually revert to a prior known-good build and then update to a fixed build.

For example:

• Office add-ins have intermittently failed to load or deploy due to Exchange authentication changes, with Microsoft applying targeted mitigations and advising customers to contact Support if issues persist.
• Outlook add-in regressions (including event-based and signature add-ins) have been fixed by specific later builds or configuration rollbacks, sometimes requiring Outlook restarts to pick up corrected settings.
• Excel add-in regressions (RichApi.Error 0x8002802B) were explicitly resolved by updating to a specific or later build.

Given that reverting from 26.03.19725.20152 to 26.02.16.0.19725.20152 and then updating to 26.02.19725.20190 restores functionality in this environment, the actionable guidance consistent with documented patterns is:

1. Keep affected clients on a known-good build (in this case, 26.02.19725.20190) until Microsoft publishes a fix in a later 26.03 or newer build.
2. Monitor the Microsoft 365 Apps update history and Office/Outlook add-ins known issues pages for a note that a specific build resolves an add-in regression affecting Exchange on-prem add-ins.
3. If the issue persists or if remaining on 26.02.19725.20190 is not acceptable, open a support ticket with Microsoft, referencing:
   • The affected build (26.03.19725.20152),
   • The working build (26.02.19725.20190),
   • The impacted add-ins (Phish Alert, Zoom),
   • That this is an Exchange on-premises add-in scenario.

This aligns with existing guidance for similar add-in regressions, where Microsoft confirms the issue, rolls out a fix, and customers either revert to a prior build or update to the fixed build once available.

References:

• Office Add-ins known issues
• Outlook email is delayed while a web add-in is working on the send request
• Debug Office Add-ins on a Mac
• How can I get office 365 to work? - Microsoft Q&A
• Office 365 apps insist on using Outlook Classic to share documents to email - Microsoft Q&A
• Unable to add apps within Outlook, get "Something went wrong" generic error message - Microsoft Q&A
• My Microsoft365 Office Package no longer works with my iPad Pro - Microsoft Q&A
• Run Time Error 438 in Excel Sheet - Microsoft Q&A