How To Search All Mail Folders in the Mail App
The Mail app bundled with Mac OS X features a search tool that allows you to rapidly search for specific email messages in your mail folders (Inbox, Drafts, Sent) or all mailboxes. Content from Junk, Encrypted or Trash are normally excluded from the search results, but if the need arise you can configure the Mail app to search these locations too. Display Results from Trash, Encrypted ... Folders when Searching the Mail app
Open the Mail app, click on the Mail menu > Preferences > General tab. Move to When searching all mailboxes, include results from and then tick the checkboxes next to Trash, Junkand Encrypted Messages.
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