Marketo sales insight "Email" tab shows the list of emails that you've published to sales insight,
This is not correct, I am afraid. The email tab shows all the emails and sales emails that have been SENT to the lead or contact.
AFAIK, there is no notion of delivered in Sales Insight.
Most systems cannot really tell you if the target server responded OK. As long as the server did not actively Reject the email, it is considered Delivered. Tell Sales to worry about Clicks or Opens for Sales Emails.