First, check your email settings. Some email providers may automatically mark messages as read when they are opened.

Here are some steps to take to troubleshoot:

1. Check your email settings to see if there are any options related to automatically marking messages as read.
2. Check to see if you have any add-ons or extensions that may be causing the issue.
3. If you have multiple devices, make sure that all of them are set to the same settings.
4. If you are using an email client, try using the web interface instead.

If none of these steps work, contact the email provider to find out more about the issue you are experiencing.