Email marketing metrics can provide valuable insights into the success of a campaign. Commonly used metrics include open rates, click-through rates, and unsubscribe rates.

Open rates measure how many people opened an email compared to the total sent out. Click-throughs measure how many people clicked on a link in the email, while unsubscribes measure how many people are no longer interested in receiving emails from that company.

Other important metrics include list growth rate (the number of subscriptions over time), delivery rate (the percentage of sent emails that were accepted by ISPs or recipients' mail servers), and conversion rate (the percentage of recipients who completed an action following an email). By understanding the data behind these metrics, businesses can get a better idea of what is working in their email campaigns and make adjustments accordingly.