Click on CONTACTS to see your lists and associated STATISTICS.
You can sort your contacts by mobile number, date added or name order by clicking the COLUMN HEADERS at the top of each columns.
OPTING-OUT a recipient will not allow you to import that number back into the list while just deleting a number will.
DELETING a recipient will not opt them out of your list, if you re-import the same number it will be re-added.