There are several threads on this, please do a search.
Please keep in mind to refresh your list and report because some leads may be Pending. Generally the total Sent will be the same, however, Clicks and Opens may differ for a variety of reasons.
- spam filters clicking links and opening
- image blockers
- people who click several times vs. # of people who clicked at least once.
And also because Marketo is reporting Opens when the person clicks, event if the open event is not logged into the activity log (meaning the pixel tracking has not been downloaded). In this case the Number of opens in reports is higher than what the "Opened email" smart list shows.