This depends on the settings of the deduplication process. Deduplication is done by default based on an email address. This means that when a contact in your list has the same email address as the existing contact in Spotler, the details of the existing contact in Spotler will be supplemented and /or possibly overwritten with the details in your file. Therefore, it is always good to check which system or file contains the most up-to-date details, so you do not overwrite new details with old details.
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