Send & Track email from Outlook - which IP?

If someone is sending an email through Outlook, but uses the Send & Track button from the sales insight plugin, which IP is it sent from? Corporate IP or Marketo IP? If someone unsubscribes or has hard bounced from Marketo emails, I want to make sure the 1:1 sales emails still go through from Outlook. The ones from CRM do not go through because it's sent from the Marketo IP. Can't seem to find information on this anywhere. Thanks in advance!