emails disappearing

Hi,

I have a desktop, laptop, and iPhone. Whereas emails remain visible on my laptop until I delete them, many in the same account are no longer visible on my desktop after I read and close them. The account settings on my laptop and desktop are the same, except there is an addtional option on my desktop that is not on my laptop, TSL Certificate. This is set to "none."

Any ideas how I can access my emails on my desktop. Again, they are there on my laptop, but they disappear from my desktop after I read them.

Thanks.

Steve

P.S. They are set up as imap accounts