Duplicate rule actions on create and edit
Key Takeaway
A duplicate rule decides whether a user can save a record that matches an existing record: "Allow" lets the save happen and "Block" stops it. On edit, the rule runs only when the edited fields are part of its matching rule.
A duplicate rule tells Salesforce what to do when a user creates or edits a record that looks like a duplicate of an existing record. The rule can let the user save the record anyway or stop the save. The rule can also show an alert and report the duplicate so it can be tracked. Admins use duplicate rules to control whether and when reps can create duplicate accounts, contacts, and leads.
Duplicate rules and matching rules
A duplicate rule always works with a matching rule. The matching rule decides how records are identified as duplicates. The duplicate rule decides what happens when a user creates or edits a record that matches.
Each duplicate rule can hold up to three matching rules. You can activate a duplicate rule only when all of its matching rules are active.