Yes. Users can turn on or off the Highlight and search option from the Prefereces menu:
1) Click on the Preferences menu.
2) From the Email Section, cilck on General Settings.
3) Within the Viewing emails category you will see the option for Highlight & Search.
4) Select the on or off button and click, SAVE.
NOTE: This feature can also be disabled when highlighting a word or phrase in email. Simply, click on the "Disable highlight and search" section of the pop-up menu.