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DLP users getting the error: "An add-in prevented this message from being sent. It will be saved as a draft."

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Article ID: 256032

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Updated On:

Products

Data Loss Prevention Data Loss Prevention Data Loss Prevention Endpoint Suite Data Loss Prevention Endpoint Prevent

Issue/Introduction

When the macOS Outlook On Send Add-in is installed on Windows machines, when the user sends an email and quickly moves to another email, the following error occurs:
"An add-in prevented this message from being sent. It will be saved as a draft."

Environment

Steps to Reproduce

Select an email with an Outlook Preview Pane enabled

Reply to the email
Immediately select another email

Cause

Customers deployed the "On-Send Web Add-in for Outlook on Windows endpoints due to users having both Windows and MacOS systems 

Deploying the on-send web add-in for Outlook on macOS endpoints

 

Resolution

Download and install the Microsoft Administrative templates from Microsoft: Download Administrative Template files (ADMX/ADML) for Microsoft 365 Apps for enterprise/Office LTSC 2021/Office 2019/Office 2016 and the Office Customization Tool for Office 2016 from Official Microsoft Download Center


In Group Policy Editor, navigate to User Configuration > Administrative Templates > Microsoft Outlook 2016 > Miscellaneous > Deactivate Outlook web add-ins whose equivalent COM or VSTO add-in is installed
Set this to Enabled, and add the following entry:
Value Name: e9c6b99a-5fef-434d-b3e5-f4d5883723b1
Value: Otlk.OutlookAddin