Single Click instead of Double-Click?

I'm using an Intel iMac running snow Leopard. When using Apple mail I have always been able to single click to read the e-mail. Now, I have to double-click. I have neurological impairments along with carpal tunnel syndrome. I have been doing some Google searches on this issue but so far no solutions to this problem. I am buffaloed. This double-click stuff is a PITA. By the way, I'm using a Kensington expert trackball mouse. No options for single click. I don't think the mouse has anything to do with this problem. Computers up to date with the latest software. I did rebuild Apple mail.

On my MBP with the trackpad it is still a single click are you sure in your mouse settings in system preferences you can't change this .

I have gone into Preferences > Mouse, but I cannot find any option for single click. It always single clicked by default in the past. Now I have to double-click. I don't know?

Double-click opens a message in a new window. Have you hidden the preview pane somehow?
Single-click will show the message in the preview pane.

cradom said:

Double-click opens a message in a new window. Have you hidden the preview pane somehow?
Single-click will show the message in the preview pane.

Click to expand...

It's possible. Can you explain to me where I can find the "preview pane"? I have looked but was unable to find, e.g. preview pane.

ETA: I also noticed when I double-click on a new e-mail a 2nd box appears with the sender's message. This did not happen before. WTH? Any ideas?? Also, I did a Google search for preview pane but it didn't help very much.

Screenshots Below.

I'm on Lion which has 3 paned view by default. Don't remember how Snow Leopard's mail did it.
Try looking in View menu or prefs for number of panes...
Wait - just Googled it and found this: Mac OS X Mail: How to show or hide the preview pane or mailboxes drawer
Look in your first pic - just under "4:00Pm" - drag the little double lines up.

cradom said:

I'm on Lion which has 3 paned view by default. Don't remember how Snow Leopard's mail did it.
Try looking in View menu or prefs for number of panes...
Wait - just Googled it and found this: Mac OS X Mail: How to show or hide the preview pane or mailboxes drawer
Look in your first pic - just under "4:00Pm" - drag the little double lines up.

Click to expand...

YES! Thank you!