Nokia :: 5800 Automatically Deletes Emails From Server Once Read

I am having problems with my email in my 5800 can anyone help?it has worked perfectly since I had it until January when it suddenly decided to download every email I have ever kept on my server (several hundred) I then had a fiddle with the settings and now once it picks up my emails and I've looked at them it automatically deletes them from the phone and the server without asking even though I've checked the 'always ask button' I have lost several very important documents this way. I have previously not had this problem in fact when I deleted e-mails before this problem and hit the 'delete from phone and server' the e-mail still remained in my home computer. I have gone through all the settings on the phone many times and cannot see why this should be happening.