Bounces are addresses which return a message. The message is a notification sent by the system, which indicates that the recipient is unavailable.
If we receive three consequent bounces from the address, and the time between each bounce is more than seven days, the address is deactivated. However, this policy might be applied more strictly for some email providers.
Delivering newsletters to malfunctioning addresses negatively affects sender reputation. Purpose of the practice is to improve our customers’ message deliverability.