Please follow below steps to search your keyword in an email’s message body/text in Outlook.

1. Shift to the Mail view, and double click to open the email whose message body you will search the keyword in.

2. Click Message > Find. See screenshot:

3. In the opening Find and Replace dialog box, please type the keyword you will search into the Find what box, and then click Reading Highlight > Highlight All. See screenshot:

And now the specified keyword in the message body is highlighted, but not highlighted in message header. See screenshot:

4. Close the Find and Replace dialog box.

One click to enable Query Builder, and easily search with multiple keywords In message body

Kutools for Outlook can help you enable the Query Builder in Advanced Find dialog box with only one click. Under the Query Builder tab, you can add multiple search keywords, and specify the logical relationship "AND" or "OR" amount these keywords. 

If you need to search the specified keyword in the message bodies/text of all emails in a certain mail folder, please do as follows:

1. Shift to the Mail view, and open the specified mail folder where you will search keywords in message bodies of all emails.

2. Press Ctrl + Shift + F keys simultaneously to open the Advanced Find dialog box.
Note: You can also open the Advanced Find dialog box by putting cursor in the Instant Search box and clicking Search > Search Tools > Advanced Find.

3. In the Advanced Find dialog box, please go to the Advanced tab, and define search criteria:

(1) Click Field > All Mail fields > Message;
(2) Select the contains from the Condition drop down list;
(3) Type the specified keyword into the Value box;
(4) Click the Add to List button.

And now the defined search criteria is added into the Find items that match these criteria box.

4. Click the Find Now button.

all emails whose message bodies contain the specified keyword are found out and listed at the bottom of Advanced Find dialog box. See screenshot:

5. Close the Advanced Find dialog box.

Search entire specific phrase in Outlook

Search for an exact match to character strings/phrase in Outlook

Search with wildcard in Outlook

Search words within attachment (content) in Outlook