Outbound Glossary
Deduplication
Removing the same company or person appearing twice. Skip it and one prospect gets your campaign three times, from three mailboxes.
Deduplication collapses duplicate records that arrived from different sources, where the same company appears under a trading name, a legal name and a domain variant.
In outbound the cost of failure is visible to the prospect. Duplicates across lists mean one person receives the same approach several times, sometimes from different senders on your side, which reads as either incompetence or a bought list. Match on domain rather than name, because names are written many ways and domains are not.