The trick is in using the "Reports" function - Here's How...

In the Admin console:

1. If your mailing list does not exist then go to Marketing > Lists and create one
2. Go to Reports > Create a Customer Report
3. Select "Create a new Customer Report" from the Action Box on the right
4. In "Choose Report Type" select "Contacts Only"
5. Click Next
6. The only field that is required is Email 1 (Primary) however First Name and Last Name often come in handy so select them too
7. Click Next
8. The Filter by selectors are where we narrow down our selection from all customers in the database to just the ones we want to go into this list
   - If you have segmented your database using Customer Type or Industry (or one of the dozen or so other selections) then use that to specify the record set you wish to send to
   - You can also filter by custom fields you might have set
9. Click Generate Report
10. Check that the listing you have generated is what you expect from the system
11. If everything is OK then click Add Customers To and click Campaign List and select the list you want to add them to in the dropdown
12. Click Submit
13. You should get a message indicating that the customers have been successfully added to the list

You can now check Marketing > Lists to verify that you have the right recipients and then create your email campaign.