Receive email while Outlook 2k is closed

I have a customer that is using Outlook 2000 on a Win98 machine at home with a pop3 account through a DSL ISP. She says that when she closes Outlook she can still receive email and that it eventually uses up all her system resources. I have looked in all the my settings for Outlook 2000 and can’t find any setting to keep the email account open but hidden. When she ctrl>alt>del she can close outlook and everything is fine. Is there a third party add on that will do this or is there a setting that I am missing.