When an email promo cannot be delivered to an email address, it’s called a bounce. There are lots of different reasons why promos can bounce so, when it happens, a “return to sender” message (or, SMTP reply) is sent from the recipient’s mail server to explain why. Promo.ly will display this information in your activity log. We recommend reading this support article about free list analysis.
Updated on: 08 / 08 / 2019