If you can’t for some reason enable the Clutter option within the Outlook portal (https://outlook.office.com) because the option just isn’t there, there is a very simple way to enable Clutter via the use of PowerShell.  This should only be done by your system administrator, so please ask them 🙂

# Prompt for credentials
$UserCredential = Get-Credential

# Create the session to Microsoft Exchange Online
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
Import-PSSession $Session

# Enable Clutter on mailbox
Set-Clutter -Identity joe.bloggs@contoso.com -Enable $true

# Disconnect from Microsoft Exchange Online
Remove-PSSession $Session