Before you selecting the recipients, please ensure the mailing list is fine in the List Manager.
To select recipients for the active project. Click Recipients on the project view header and select the To Mailing List and To List Group.

Refresh
Reload the receipts from the list source.
Preview Message
Previews or sends the personalized message for the selected receipt. You may
also do the job by double click the recipient row.
Import
Imports contacts from Outlook, Excel, Access or other medias to the list.
Export
Exports the contacts of the list to Text, CSV, Address Book files or other medias.
Manage Lists and Groups
Switches to the List Manager of the
selected mailing list.