Use Thunderbird,

+Install
+Add your email (doesnt matter , you can remove it right after), close Thunderbird
+ Go to User/Yourname/Appdata/Roaming/Thunderbird/profile/Mail/  (not to be exact but you will figure it out)
+copy your mbox file to that folder
+  Reopen Thunderbird,
+ you now can remove your email account (right click on your email address tab)
+ wait for the mbox being imported.
+ click on the name of the mbox tab, enjoy and full feature of an email client. (Search sort,...everything)

Have fun digging.