Only contacts that are assigned to the MM-eMag category in Mercury would have been sent the eMag (Premium only). Your contacts are not automatically assigned to the MM-eMag category.
You will need to assign your contacts to their relevant categories (MM-rba, MM-eMag or MM-sms) as part of your initial set up for the Digital Marketing Hub so that they can be included in the eMag send.
Refer to our Wiki resources below:
If you have assigned contacts to the eMag category and they were not sent the eMag, let us know and we will investigate.