I do not use Outlook as my e-mail client, so I do not know the exact situation. However....

The e-mails are kept at the mail server at your ISP, not the Inbox of Outlook.

At Tools-->e-mail accounts, choose yours and go to properties. Somewhere there is an option to keep the e-mail at the mail server for a number of days, or just " keep a copy at the server". Here, the computer (Outlook)you are using tells the server not to delete the mail after being downloaded and read. If you then use another conputer to download the mail, it will be deleted from the server, unless you have also made the option to keep a copy at the second computer.

Some ISP also provide a web based e-mail linked to your POP account where you can access your mail. You choose whether to delete or not to delete your mail there. Try enquiry at support at your ISP.

What I have described is what can be done with "Outlook Express". With Outlook, it is similar, yet quite different. Please wait for someone with Outlook to come along...