It could mean some of your visitors don’t trust you enough to share their correct email address with you. So the first thing you’ll want to do is to see how you can improve your site and make it appear more trustworthy.
Secondly, be sure to follow your promise of not sending too many emails that will choke the recipient’s inbox.
Thirdly, if you are using purchased lists, stop doing that. Such lists have a higher proportion of temporary email addresses and spam traps.
Next, consider reviewing the security levels of your website because, as mentioned earlier, DEAs pose a security threat.
Finally, verify email list and unsubscribe such addresses.