Mouse stopped working in mail preview pane
After first mail message I read each time I open Mail, I lose the functionality of my mouse. No highlighting, no quick peek, no copying.
Commands work: I can use CMD+A to highlight everything for example.
If I forward the mail message, I regain all functionality in the active window (ie, in edit mode, not read mode).
This is new behavior.
I'm running El Capitan OS X 10.11.6
Is there a possibly corrupt file I can delete?
iMac Pro