You can search across all your emails, including sent emails, from the Global Search function.
From here you can search for any email across subject, sender, recipients, text or attachment files.
If a search term containing more than one keyword does not produce any results, the same search query will be re-run with all keywords optional. You will then see results that contain at least one, but maybe not all, of the keywords.
Clicking on an email will open it in a new tab of your browser.