How do I delete my Master List?

It's not possible to delete the Master List but you can delete all email addresses from your account. Follow these steps.
 
First, download all list members in your account
 

1. Click Lists
2. Click the Actions link to the right of the Master List and select Download Members
3. For What to Download, select All List Members
4. For File Format, select Comma Delimited (.csv)
5. For List Fields, select Click on Email Address Only
6. For Send Notification, enter your email address
7. Click Download
8. Your list will be emailed to you, when received open the file
9. Delete all columns and headers (including the email header) leaving only the individual Email Addresses (the file will be rejected if there are any other columns or headers present)
10. Save the file

 
You will next use the file to purge your Master List. This will permanently delete all records in your account.
 

1. Click Lists
2. Click on the Master List.
3. Click on the Tools tab
4. Click Mass Update
5. Click Browse and locate the file you saved
6. Click Delete from account (this is permanent!)
7. Process File and Done