Essentially there are two cases we check for duplicates when importing the leads to your campaign:
1. Check for duplicate emails across all Campaigns/Lists/Workspaces.
This can be achieved by ticking these checkboxes when importing leads.
Check for duplicate emails across all Campaigns
If you want to import a lead that has already been imported into any other campaigns, you can then uncheck the option.
Check for duplicate emails across all Lists
If you want to import a lead that has already been imported into the lists, you can then uncheck the option.
Check for duplicate emails across all Workspaces
If you want to import a lead that has already been imported in any of your workspaces under this Instantly account, you can then uncheck the option.
2. 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.