The email forwarding rate represents the proportion of people receiving an email who choose to forward or share it with someone else using the dedicated function in their email client. This action can be interpreted as a sign of interest in the message’s content, thus reflecting its quality. In practice, only email service providers are able to directly measure the forwarding rate, and some of them use it as a criterion for filtering spam or prioritizing emails. Another way to measure this rate is through research panels. On the sender’s side, forwards can be detected by observing repeated opens of the same email from different IP addresses or devices. Evolving behaviors, with emails being accessed on various devices, have made this analysis more complex. It’s important not to confuse the forwarding rate with the sharing rate, which can be measured by a specific feature of the sending platform. To illustrate, 2015 data collected by Return Path from panels provides an overview of some forwarding rates observed at that time.