You don't have to choose a specific list to send an email to. You can send an email based on certain criteria. For example, in the Smart List of a Smart Campaign drag in a Filter for Industry and select Apparel to send an email to all leads with Apparel in that field. Think of what all your leads have in common and enter that in the Smart List as best you can. Did they all fill out a form? If so, use the filter for "Filled Out Form."