Update retention policy shared mailboxes

Connect-ExchangeOnline -showBanner:$false

$PolicyName = "Shared Mailboxes Retention Policy"
 
If ([Environment]::UserInteractive) {
    # We're running interactively...
    Write-Host "Script running interactively... connecting to Exchange Online PowerShell" -ForegroundColor Yellow
    [array]$Modules = Get-Module | Select-Object -ExpandProperty Name
    If ("ExchangeOnlineManagement" -Notin $Modules) {
        Write-Output "Connecting to Exchange Online..."
        Connect-ExchangeOnline -showBanner:$false
    }
    Write-Output "Connecting to Security & Compliance Center PowerShell..."
    Connect-IPPSSession -ShowBanner:$false
} Else {
    # We're not, so likely in Azure Automation
    Write-Output "Running the update retention policy for Microsoft 365 shared mailboxes in Azure Automation"
    # Fetch the account credentials to use
    $O365Cred = Get-AutomationPSCredential -Name "AzureExchangeOperations"
    Connect-ExchangeOnline -Credential $O365Cred -DisableWAM
    Connect-IPPSSession -Credential $O365Cred
}
 
# Look for the Microsoft 365 retention policy for shared mailboxes
$Policy = Get-RetentionCompliancePolicy -Identity $PolicyName -DistributionDetail -ErrorAction SilentlyContinue
If ($Policy) {
    Write-Output ("Found retention policy to update: {0}" -f $Policy.Name)
} Else {
    Write-Output ("No retention policy named {0} found" -f $PolicyName)
    Break
}
 
Write-Output "Looking for shared mailboxes in the tenant"
[array]$SharedMailboxes = Get-ExoMailbox -RecipientTypeDetails SharedMailbox -ResultSize Unlimited
If ($SharedMailboxes) {
    Write-Output ("{0} shared mailboxes found" -f $SharedMailboxes.Count)
} Else {
    Write-Output "No shared mailboxes found" -ForegroundColor Green
    Break
}
 
# Find the current locations for the retention policy
[array]$Locations = $Policy.ExchangeLocation.ImmutableIdentity | Sort-Object
[array]$NewLocations = $null
[array]$RemovedLocations = $null
 
# Check each shared mailbox to see if it is already in the retention policy and add it if not
ForEach ($Mbx in $SharedMailboxes.ExternalDirectoryObjectId) {
    If ($Locations -notcontains $Mbx) {
        $DisplayName = $SharedMailboxes | Where-Object { $_.ExternalDirectoryObjectId -eq $Mbx } | Select-Object -ExpandProperty DisplayName
        Write-Output ("Shared mailbox will be added to retention policy: {0}" -f $DisplayName)
        $NewLocations += $Mbx
    }
}
 
# Check each location in the retention policy to see if it is still a shared mailbox and remove it if not
ForEach ($Location in $Locations) {
    If ($SharedMailboxes.ExternalDirectoryObjectId -notcontains $Location) {
        $DisplayName = Get-Recipient -Identity $Location -ErrorAction SilentlyContinue | Select-Object -ExpandProperty DisplayName
        If ($DisplayName) {
            Write-Output ("Shared mailbox will be removed from retention policy: {0}" -f $DisplayName)
        } Else {
            Write-Output ("Shared mailbox with identifier {0} not found in the tenant and will be removed from the retention policy" -f $Location)
        }
        $RemovedLocations += $Location
    }
}
 
[int]$NewLocationsCount = ($NewLocations.Count + $Locations.Count - $RemovedLocations.Count)
# Check if the additions and removals will create more than 1,000 locations in the retention policy
If ($NewLocationsCount -gt 1000) {
    Write-Output "The retention policy will have more than 1,000 locations after the update."
    Break
} Else {
    Write-Output "The retention policy will have $NewLocationsCount locations after the update."
}
 
# Do the actual work to remove and add locations - depending on what we found, we issue the appropriate command
If ($RemovedLocations.count -gt 0 -and $NewLocations.count -gt 0) {
    Write-Output "Updating locations for retention policy $PolicyName"
    Set-RetentionCompliancePolicy -Identity $Policy.Name -RemoveExchangeLocation $RemovedLocations -AddExchangeLocation $NewLocations
} Elseif ($RemovedLocations.count -eq 0 -and $NewLocations.count -gt 0) {
    Write-Output "Adding locations to retention policy $PolicyName"
    Set-RetentionCompliancePolicy -Identity $Policy.Name -AddExchangeLocation $NewLocations
} ElseIf ($RemovedLocations.count -gt 0 -and $NewLocations.count -eq 0) {
    Write-Output "Removing locations from retention policy $PolicyName"
    Set-RetentionCompliancePolicy -Identity $Policy.Name -RemoveExchangeLocation $RemovedLocations
} Else {
    Write-Output "No changes to make to retention policy $PolicyName"
}
 
# And remove any Exchange retention policies from the added shared mailboxes
If ($NewLocations) {
    Write-Output "Updating mailbox settings to remove Exchange MRM policies from shared mailboxes newly added to the retention policy"
    ForEach ($Mbx in $NewLocations) {
       Set-Mailbox -Identity $Mbx -RetentionPolicy $null
    }
}
 
Write-Output "Task completed. The retention policy $PolicyName has been updated for shared mailboxes."