To delete a mailing list, go to PoliteMail > Lists > Mailing Lists.
Check the box next to the list you wish to delete.
Click the X button.
You will now be given a warning asking if you are sure you want to delete. If you choose YES, you will be brought to another window, asking if you want to delete all contacts and associated tracking.
If you click Yes, the contacts and their tracking results will be deleted from ALL mailing lists if you're using Individual Tracking Modes. If you use Anonymous or Aggregate tracking, your metrics will be safe and just the contacts will be deleted. As a best practice, choose NO on this window. This way, PoliteMail will delete this individual list, but still keep contacts who may be on other lists.
You can also use this X to delete individual contacts within a list.