The reality is that there will always be email subscribers who choose to unsubscribe from newsletters. The good news is that on average only about 0.25% of subscribers choose to unsubscribe. If your unsubscribe rate is a lot higher, try to make your content less promotional. You could also try to send emails not as often. If you send an email after a subscriber has unsubscribed, you can also give them the option to subscribe only for certain types of emails.