Perform the following steps:
Open the message that you want to search.
Alternatively, check that the preview pane is displayed, then select the message that you want to search.
Choose Edit -> Search Message.
Type the text that you want to search for in the Find text box in the Find in Message dialog. To make the search case sensitive, select the Case Sensitive option.
Click Find. The matches are highlighted in the message. The total number of matches is displayed in the Find in Message dialog.
To close the Find in Message dialog, click Close.