Yosemite operating system - mail I want to show previews of my mail. There was a tip to drag on the thick vertical line but i don't see where that is located. I have already unclicked the classic layout view in preferences and can see my mail topics but there is no viewing preview to the right, where i would like it to be.
Please try this.  Click on Mail > Preferences > Viewing  There will be a dropdown for list preview.  Select a choice other than None.  That will give summary information about the email message you have selected. Make sure you select an email. The actual email message should appear to the right of the summary.  If it does not, you'll probably need to move your cursor as far to the right of the screen as you can go.  Push down your mouse or track pad and move the cursor to the left.  You should see the email that is selected.