How to determine whether a custom deduplication rule will create a new lead or update an existing lead.
TestField (without email address):
TestField and Email Address are present:
Lead 'A' has a email address value of: 123Test@Test.com
Lead 'A' has a TestField value of: 000111
Lead 'B' has a email address value of: 123Test@Test.com
Lead 'B' has a TestField value of: 123456
Lead 'A' would create a lead record with a duplicate email address as both fields did not match what was on the existing lead in the database.
Lead 'B' would update the existing lead in the Marketo database due to both fields matching the existing lead record.
Email Address (without TestField):
All leads(with no TestField value present) would create new lead records within the Marketo database. A blank, or empty value is still seen as a value in Marketo.