Duplicate leads are two or more leads we think is the same lead.
We match leads on whichever fields each list is configured to match on, and if we find matches, we mark the matching leads as duplicates.
Every list starts out matching on both phone numbers and email addresses. Two leads sharing any phone number, or any email address, are treated as duplicates until you change that. You can also pick one further field to match on — a company registration number, an account reference, or any other field you have created — and two leads sharing a value in that field will be flagged as well.
This default is worth knowing about, because it is the most common reason for a list that reports far more duplicates than it should. If the data you imported carries a shared contact detail — a switchboard number, or one address like info@ repeated on every record because it came from the data source rather than from each individual company — then every lead carrying it will be reported as a duplicate of every other. The fix is to switch off the matching you don't need and leave only a field that is genuinely unique per lead.
Misconfigured field types cause the same problem. If fields like "Email open" or "Email bounced" are set to the 'Email' type instead of a boolean type such as 'Yes/No' or 'Standard', duplicate detection will match on them and flag entries unnecessarily.
You can change all of this from your list configuration: open the configuration page for the list and go to the 'Dedupe' tab. Changing these settings clears the duplicates already recorded for that list and detects them again from scratch, which takes a while on a large list.
Best Practices for Avoiding Duplicate Warnings
Regularly audit your field settings to ensure all fields are correctly assigned appropriate types.
Test adjustments on a sample list to ensure configurations work as intended before applying them system-wide.
Use specialized field types, such as 'Company' for grouping by organization, to reduce erroneous matches.
You can view and manage duplicates from Manage => Duplicates or when viewing the individual leads (when calling them).
Whenever a lead has one or more detected duplicates, myphoner shows a duplicate tab when viewing that lead. From the duplicate tab you can decide how to handle the situation, either by deleting one or more leads, merging them or ignoring the problem. Understanding why duplicate warnings appear can help ensure accurate handling. Misconfigured fields, such as assigning the wrong field type, may result in unnecessary duplicate warnings, highlighting the importance of reviewing list configurations.
See also Merge (two leads).
The duplicate warning tab let you easily compare and handle duplicates.
Note: you can also bulk deduplicate leads instead of working them one at a time.