The marketing team at UVC has a list of 400 leads it wants to upload...

The best actions to take to avoid creating duplicate leads when uploading a list of 400 leads are to utilize a Lead Matching Rule and corresponding Duplicate Rule to block newly created duplicate leads, and to upload the lead list using the import wizard and select a Matching type to prevent duplicate lead creation. The Lead Matching Rule defines the criteria for identifying duplicate leads, and the Duplicate Rule defines the actions to take when a duplicate is detected. The import wizard allows users to choose a Matching type based on the Lead Matching Rule and block or allow duplicates. Using Data Loader’s update function or enabling Duplicate Matching in the Data Management section will not prevent duplicate lead creation.