Uploader crashed, still need to finish uploading but duplicate emails?

[Mark Schilling]

I was uploading a inbox with the Mac uploader that has over 20k emails.  The uploader crashes after 17k+ emails migrated.  We need to migrate the rest of the emails, but will all the emails that were already migrated be duplicated on the google account?  Or does the uploader compare the index file of each email and skips it if already found on the google account like the Outlook migration tool does for Windows?  I don't want to start the migration again for the mac and get 17k+ duplicate emails considering that was already 14 GB of data to upload.