1. Launch powershell and run the commands below
2. Set-ExecutionPolicy RemoteSigned
Choose yes.
3. $UserCredential = Get-Credential
put your email address of your domain admin account and its password
4. $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection
5. Import-PSSession $Session
6. Get-Mailbox | Set-Clutter -Enable $false
once done.
Be sure to disconnect the remote PowerShell session when you're finished. If you close the Windows PowerShell window without disconnecting the session, you could use up all the remote PowerShell sessions available to you, and you'll need to wait for the sessions to expire. To disconnect the remote PowerShell session, run the following command.
7. Remove-PSSession $Session