The E-mail Exposure ‘Ceiling’: Ways to Measure and Make it Work

* Track unsubscribe rates closely. “Generally, an unsubscribe rate greater than 1 percent on a house list means you’ve crossed the line,” Kapur says. That’s because every unsubscribe cuts into your potential target base.

He cites a travel company that averaged an unsubscribe rate of 0.7 percent when sending three e-mails a month to its house list. The company then tested five e-mail messages a month. But by the time the fourth e-mail hit, the unsubscribe rate inched up to 0.8 percent and grew to 1.1 percent after the fifth e-mail was sent. By the second month of testing, the company had decided its exposure ceiling was four e-mails a month. Sending the fifth email had resulted in a negative net effect, Kapur notes.