Keep email on original server

I just purchased a new MacBook Air. Like others in this group, now I cannot keep the original emails on my server. I have 2 other computers I need to be able to download the emails and for work, need to keep them on the server. It's not just that they are deleted, they disappear. I cannot use Mail at all now. I have seen different suggestions using imap, pop or other downloads but cannot get them to work. Why can't Apple just bring back the simple click option to keep emails on the server?