To measure the effectiveness of combining data in email marketing, track the following metrics: - Open Rate: Indicates the percentage of recipients who open your email. - Click-Through Rate (CTR): Measures how many recipients clicked on links within your email. - Conversion Rate: Tracks the percentage of recipients who completed a desired action. - Bounce Rate: Monitors the number of undeliverable emails. - Unsubscribe Rate: Indicates the number of recipients who opted out of your email list.