The Search module vastly improves the search capabilities of the quick search top bar. Click the ADVANCED FILTER button to open a dialog that will help you refine the search criteria on all your e-mails.
You can combine multiple search criteria, some of which are inclusive or exclusive (i.e., you can search for e-mails with or without attachments, that are flagged or not, and that are read or unread), while other allow to provide values for almost any other property of an e-mail, including sender or recipient, subject or keywords, type of attachment, and limit the search according to a period of time or to a size interval.
Moreover, you can search on tags given to the e-mail and limit the search to specific folders. When all criteria have been entered, click SEARCH to start the search, while clicking RESET will clear the dialog.
In the resulting list of result, click any e-mail to open it. To further refine the search, click the blue bar above the list of e-mails. The dialog will reopen, with the same criteria entered before: here you can add more constraints or change some of them.