🚀 Overview

IT Administrators may encounter a specific synchronization error where delegates, operating in Cached Mode within Microsoft Outlook 2016, are unable to finalize meeting requests on behalf of a delegator. This issue typically manifests when a delegate initiates a meeting on another user’s calendar, utilizes the Scheduling Assistant, and then integrates a Skype or Teams meeting link after the item has resided in the Drafts folder for an extended period.

The core of the issue lies in a versioning conflict between the meeting data held in the local system memory and the version synchronized within the local cache. When the delegate eventually attempts to send the invitation, Outlook identifies that the message has been modified background-side, triggering a failure in the “save” portion of the process even if the “send” portion succeeds.

⚙️ Key Technical Details

• Conflict Trigger: The error is rooted in the Exchange Based Assistants (EBAs). These service-side assistants may write changes to a meeting item while it is still in a draft state. If the Outlook client attempts to send the meeting after these background changes occur, a conflict resolution failure occurs.
• Autosave Mechanism: By default, Outlook is configured to automatically save message drafts every three minutes. Once a meeting is autosaved to the Drafts folder, it becomes eligible for processing by EBAs or ItemAssistants.
• Two-Phase Processing: Outlook handles meeting invitations in two distinct stages:
  1. The physical saving of the item to the calendar provider.
  2. The transmission of the invitation to recipients.

  In this specific failure state, the invitation is successfully dispatched to attendees, but the “Save” operation to the delegator’s calendar fails due to the version mismatch.

• Third-Party Add-ins: While native Teams and Skype add-ins are the primary focus, the same behavior can be triggered by third-party conferencing tools that modify the meeting body or metadata after the initial draft creation.

⚠️ Impact

When this conflict occurs, delegates will receive the following error message:

“Changes to the meeting cannot be saved. The meeting has been updated by another person. Close and reopen the meeting, and then make your updates. The operation cannot be performed because the message has been changed.”

Administrative Implications:

• Calendar Inconsistency: The meeting will not appear on the delegator’s calendar, creating a discrepancy between the organizer’s schedule and the attendees’ schedules.
• False Positives: Because the “Send” operation succeeds, attendees receive the invite and may accept it, unaware that the organizer’s calendar does not reflect the appointment.
• User Experience: Delegates may spend significant time drafting complex meetings only to find they must restart the process if the draft was open for several hours.

🛠️ Workarounds and Resolution

🛡️ Immediate Workarounds:

• Modify Autosave Behavior: Admins can instruct users to disable or extend the Autosave timer to prevent premature draft commits. Navigate to:
  
  File > Options > Mail
  
  Under the Save Messages section, uncheck Automatically save or increase the delay to a higher value (e.g., 10 minutes or more).
• Use Outlook on the Web (OWA): This issue does not affect OWA, as it does not rely on the local cached mode synchronization logic that triggers the EBA conflict.
• Timing: If a draft is saved, ensure the invitation is sent within 90 minutes to stay within the current suppression window for background assistants.

📅 Service-Side Resolution:

A formal fix was introduced in service build 15.20.2730.00 and subsequent versions. This update modifies how the service handles notifications on meeting drafts. Specifically, it suppresses EBA and ItemAssistant modifications on draft items for approximately 1.5 hours after the initial save. This provides delegates with a larger window to finalize meeting details without encountering version conflicts.

To verify your current version, IT Admins can utilize the Connection Status dialog in the Outlook client.

Official Source: Read the full article on Microsoft.com