Prevent unnecessary sends by deduplicating email addresses in journeys. If your entry source data extension contains multiple contact keys with the same email address, deduplication ensures that each recipient receives only one copy of the email from each email activity in a journey within the specified lookback period.
Where: These changes apply to Marketing Cloud Engagement editions.
How: On the Settings page for a journey, under Journey Deduplication Configuration, turn on Enable Email Deduplication.