To search mailboxes:

Select any mailboxes you want to search. Shift-click to select mailboxes that are next to each other in the list, or Command-click to select mailboxes that are not next to one another.

Click in the Search field in the toolbar, or press Command-Option-F.

Type the text you want to find in the Search field.
Mail immediately begins to search messages in the selected mailboxes.

Narrow or widen the search results using options in the header above the results.
To change which mailboxes are searched, click All Mailboxes or the name of a mailbox you selected.
To change which part of each message is searched, choose Entire Message, From, To, or Subject. If you choose Entire Message, you can specify criteria with the text you type in the search field to narrow the results.

To save your search as a Smart Mailbox so you can easily find and view the current search results and future messages that match the search at any time, click Save.