When you launch Mac Mail Purger, you will be faced with the following screen

To set up your account, you must give the following information: pop logon name, pop password and pop server address.
If your email address is abc@def.com, then your pop logon name, entered in item 1 is "abc" most of the time, and your pop server will be something like pop.def.com or mail.def.com In doubt, check the settings in your usual email client, or contact your ISP
The pop server address (item 3) should be followed by the port number if is not the standard pop3 port (110). Again, check the settings of your email client or contact your ISP for this.
If you need to use APOP authentication, then use the check box (item 8)
Once you have entered all the information, click the button labelled "Save Settings" to create a new account. You will be prompted for a name for the account. Once you have done so, the account will appear in the popup menu (item 5). Thereafter, selecting that item from the menu will recall the settings. Please note that if you save password information as part of the settings, anyone can launch Mac Mail Purger and read or delete your messages.

Enter the settings described previously. You do not have to create an account to clear a mail box, but it will save time if you need to use Mac Mail Purger often.
Click "Purge !".The status item will provide feedback as to what is going on. Note that this will erase all the messages from your mailbox. While Mac Mail Purger is deleting the emails, the "Purge !" button changes to a "Stop" button. Clicking this will stop Mac Mail Purger, but will not bring back any messages already deleted. Don't say I didn't warn you…