Dedupely

If you're looking to deduplicate your data, before flattening it, Dedupely is one third-party integration dedicated to handling just that. Dedupely lets you adjust match settings to maximize the number of duplicates you find and customize it to handle your unique data. You can merge by hand or automatically. For most CRMs, Dedupely supports deduplication of Contacts, Companies, and Deals.
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​ https://dedupe.ly