Dynamics 365 for Marketing | Settings | Episode -02 | Form Matching Strategies by Srinath Pega

The Form matching page of the Settings, matching strategies to define how form submissions are matched to existing contacts or leads. The strategies are necessary when deciding to update an existing record or create a new one. A simple contact-matching strategy, for example, might be based on an email address alone. When a submission is received, Dynamics 365 will check if any existing contact has the submitted email address. If a match is found, the submission is used to update that contact. But if no match is found, a new contact is created with the received values. When an existing lead record is found to match an incoming form submission, the new submission becomes part of that lead's history and could affect the lead's score.