Emails sent with the Send and Track button in the Marketo Outlook Add-in are tracked like emails sent through the Marketo web interface with a few caveats.
Tracking multiple recipients
If you Send and Track an email with multiple recipients, Marketo will log all click and open activities to the first recipient in the To... field. Activity done by other email recipients will appear in the first recipient's activity log.
New leads versus existing leads
When you Send and Track an email and the recipient doesn't exist in Marketo, a new lead will automatically be created.
Marketo will do its best to identify the name and company of the lead from the email. When that's not possible, "mktUnknown" will appear in those fields. (Some CRMs will reject leads without a last or company name.) See this article for more:
When you Send and Track an email to a lead that already exists in Marketo, the email activity will be appended to that lead's activity log.
Tracking email sends
When you Send and Track an email, the add-in informs Marketo about who sent the email, who it was sent to, and what it contained (subject and body text). This shows up in a user's activity log as a Send Sales Email event.
Tracking email opens
Emails sent via Send and Track include an invisible image embedded by the add-in; when the email is opened, the email client retrieves the image from our webserver, and an Open Sales Email event is added to that lead's activity log.
Email open counts may not always be accurate. Some email clients block images which prevents tracking email opens. Also, some open counts may be inflated because a recipient may browse through their emails; each email view, however long or short, is counted as an open event.
When you Send and Track an email, each link in the email is wrapped so that Marketo is informed when a recipient clicks any of those links. These clicks appear as Click Sales Email events in the lead's activity log.
Clicking a link also cookies the recipient's browser so his web activity on your Munchkin-enabled pages is tracked by Marketo.