It’s important you monitor your bounceback rate after each email marketing campaign. Managing the bounces contributes to the list "hygiene" and meets the email marketing best practices. If you take time to monitor your bouncebacks and remove them from your list, this measure prevents you from consistently sending the emails to invalid email addresses and helps you avoid troubles with your ISP. Your email marketing service should let you read the header information from each bounced message, so you can see exactly why they bounced. You know not all bouncebacks are bad.