Hi Peopleperson49,
Thanks for reaching out using Apple Support Communities. Here to help.
We understand you're seeing an issue in your Mail app regarding an email and corresponding folder continuing to open without your prompting it to. We see how that would be a nuisance, lets see what can be done!
Firstly, is your Mac caught up on its software updates and upgrades? Falling behind here could lead to compatibility issues with third party mail accounts. The following link below will cover how to check for updates and upgrades.
How to upgrade to macOS Big Sur
Next, what type of email account is this? Is the account functioning otherwise regarding sending and receiving emails? Have you received any error messages indicating the account has connectivity issues? Knowing if the email and folder that are triggering this behavior is associated with an iCloud.com email or another provider could help us locate relevant resources.
We will provide a general resource for Mac Mail troubleshooting below, in case it can help to identify any connectivity or account configuration issues. Feel free to follow up with additional detail and we will happily assist as much as possible.
Troubleshoot email problems in Mail on Mac
Take care for now!