-To search in /tmp/mymail_2010.db and /tmp/mymail_2011.db for all mails
-having bob.something as sender or recipient, without "spam" in the
-subject
+To search in all the data-base files mymail.db located (recursively)
+in /tmp/mymail, for all the mails having bob.something as sender or
+recipient, without "spam" in the subject, and creating a result mbox
+file /tmp/mymail/mbox