Engagement Metrics: Listen for the Sound of Customers Leaving

2. Complaints (AKA This is Spam, TIS): When subscribers flag your message as spam, your email relationship is over. Not only are they disconnecting from your brand, at least in this channel, but if enough of them start complaining, they're also harming your sender reputation. Spam complaints are the clearest signal to a mailbox provider that a sender’s email is unwelcome, and a spike in complaints can trigger corrective action as providers redirect mail to spam folders (or block it from reaching users at all) to keep it from bothering their members. Marketers can use complaint rates to their advantage, however, by correlating TIS patterns with program tests. Any changes, including reductions in complaints, provide clear, fast indications of how subscribers feel about new tactics.