| Export-Csv -Path "C:\report.csv" -NoTypeInformation

defaults write com.microsoft.Outlook DisableSyncSliderForSharedMailbox -bool false

User Configuration \ Administrative Templates \ Microsoft Outlook 2016 \ Outlook Options \ Delegates .

# Get Mailbox configurations Get-Mailbox -ResultSize Unlimited | Where-Object $_.RecipientTypeDetails -eq "SharedMailbox" | ForEach-Object Get-CASMailbox).DisableSyncSliderForSharedMailbox

The registry value is a specialized configuration used in Microsoft Outlook (2016 and later) to control how much email is stored locally for shared mailboxes. By default, Outlook limits the synchronization of shared mailboxes to a specific timeframe—typically the last 12 months—to manage local storage and improve performance. Purpose and Functionality

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defaults write com.microsoft.Outlook DisableSyncSliderForSharedMailbox -bool true

When DisableSyncSliderForSharedMailbox is implemented and set to 1 , it instructs Outlook to for shared mailboxes and instead synchronize their entire contents locally. This is particularly useful for teams that need immediate, offline access to historical data within a shared environment without manually scrolling to the bottom of folders to "view more on Microsoft Exchange". Implementation Guide

There is nothing more frustrating for a helpdesk team than logging into a Shared Mailbox only to find that Outlook has arbitrarily decided to only sync the last 12 months of emails, hiding critical older correspondence. The default behavior (Sync Slider) makes sense for personal mailboxes to save disk space, but it is counter-productive for Shared Mailboxes which often act as archives.

For developers or those comfortable with API calls, Microsoft Graph provides access to mailbox settings.

This script assumes you have the Exchange Online PowerShell module installed and are connected to Exchange Online.