PersistIQ has a lot of safety checks in place. We use a strong analytics  which verify your e-mails, making sure that they are free of any errors. The analytics system also informs you on crucial activities such as making sure that your prospect have not already replied to another campaign or are in Do Not Contact list, etc.
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When you are trying to upload another list of prospects to PersistIQ duplicates will be detected and won't be added twice to the master prospects list. However, if you would like to have all of the prospects in your import you can easily go to the advanced settings and choose to update the duplicates.
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After uploading your prospects via; 

Scroll down as visible in the following video to choose to update the duplicates; 

You can also choose to update the Prospect Owner and Prospect Status.