Guide

The same person is arriving as two leads.

A duplicate is not just untidy data. Two leads for one person usually means two reps working them, or one rep working a lead that belongs to an account someone else owns.

Where duplicates come from

• A form or integration that always creates. It never looks for an existing lead or contact first.
• List imports. An event list loaded without matching.
• Duplicate rules set to alert, not block. The warning appears and is clicked through.

The duplicate you do not see: an existing account

A new lead from a company that is already a customer or an open deal is often routed round robin, to someone who is not the account owner. Match the lead's email domain against account websites and the contacts already on accounts.

Check it yourself

SELECT Email, COUNT(Id) n FROM Lead WHERE CreatedDate = LAST_N_DAYS:30 AND Email != null GROUP BY Email HAVING COUNT(Id) > 1

For each, look at the two creation sources. The one creating the second record is the entry point to fix.