Each email address is stored in a record in a mailing list database. Each mailing list has it's own database.
Searching and Results
On the main administration page is a search box where you can type in a full or partial email address and bring up a list of search results where you can click on an email address to edit it's properties and add or remove it from your mailing lists.
Once you have a search results page up, you can copy, delete, move, and perform other operations on selected email addresses by checking the boxes next to the email addresses you want to modify, selecting what you want to do in the drop down box, and clicking on the submit button.