The percentage of sent emails that fail to reach the intended recipient’s inbox is a critical metric for assessing the effectiveness of electronic direct mail campaigns. This figure represents messages returned to the sender due to permanent or temporary reasons, indicating deliverability issues. For example, if a campaign sends 1,000 emails and 20 are undeliverable, the associated metric is two percent.
Monitoring this key performance indicator is paramount for maintaining a healthy sender reputation and maximizing campaign ROI. Consistently high levels can negatively impact deliverability, leading to emails being flagged as spam. Understanding historical trends of this metric enables marketers to proactively identify and rectify issues related to email list hygiene and sending practices. Its emergence coincided with the widespread adoption of email as a marketing channel, becoming increasingly relevant as spam filters and anti-abuse measures evolved.