Why is the number of contacts that I selected to send my marketing piece to different from the number of contacts it actually went to?

This difference in numbers is most likely due to bounced, unsubscribed, and Reported Spam contacts. To check this, please go to your Contacts page. From there, click the "Options" button in the Contact box and scroll down to either “Show Permanently Bounced Contacts,” “Show Unsubscribed Contacts,” or “Show Spam Report Contacts.”