thunderbird - delete downloaded mails on the server?

currently, my thunderbird is synchronized with my mail server. meaning, if i delete a mail on the server, it also gets deleted on thunderbird and vice versa. is there a setting that i can do so that i can delete the messages on the server without them having deleted in my thunderbird inbox? when i go to tools > account settings > server settings i do not see any "keep mail on server" or "delete messages on server" options that people talk about.

I think that may only appear if you have a webmail server set up.....the Addon so you can use free hotmail accounts with thunderbird...