In order to protect both OutboundEngine's and your company's email reputation, all new contact lists must undergo a test or optimization phase to increase deliverability and reduce spam abuse.
When new contacts are added to your OutboundEngine account, our system selects a sample of your contact list (at random) to send to in order to optimize deliverability. If the majority of your list is found to be valid, the remainder of the emails will be tested over the next five days.
Any contacts affected by the test/optimization phase will be labeled as "pending" in the status column on the contacts tab of your OutboundEngine account and will not be sent an email campaign. However, barring any unforeseen issues during the testing/optimization phase, they should become active within five days.