How best to re-new my Mail...

I had to import my Apple Mailboxes [long story as to why] and it did it but then reported that it couldn't import all and that some mailboxes & messages were brought into a folder called IMPORT in the 'On My Mac" area. But now I have a gazillion of emails and probably some duplicates == just looking at them I think they may have been imported and now I have two folders, one on my mac and the other in Mail -- I don't want to have to go thru every one....I assume I can backup & move the messed up Mail folder and then turn off my Mail and other email accounts and then they'll repopulate IMAP style - OR -- I can go into TimeMachine and replace the messed up Mail with what was there before this import screwup happened....I can do either or something else but would appreciate some help in avoiding going thru and reviewing all the emails and getting rid of dups.