Check for duplicate emails across all your campaigns.

This can be achieved by ticking the checkbox "Check for duplicates across all campaigns" when importing leads. If you want to import a lead that has already been imported in other campaigns, you can then uncheck the option.

Check for duplicate emails in your original Google sheets or CSV files

This is a preventive measure so that within the same campaign, the same lead is not contacted twice with the same content. This feature can not be disabled and will always check for duplicates in that file.

You will see this error "this email already exists" if there are duplicates in that particular file hence the system has cleaned the data for you.