Hi there! I understand that you're seeing your emails listed, but when you try to open one, the screen stays unresponsive and you can't actually read the email content. I want to help you get this sorted out.

Just to clarify before we start: Are you using the Mail.com app directly on your Mac running OS X 10.15.7, or are you accessing mail.com through a web browser? Also, does this happen with all emails or only some specific ones? Any additional details can help me narrow down the cause.

In the meantime, here are some initial steps tailored for your Mac:

1. Quit and Relaunch the Mail.com app or Browser
Sometimes restarting the app or browser can clear minor glitches. On your Mac, you can quit the Mail.com app by pressing Command + Q. If you use a browser, simply close the tab or window and reopen it.

2. Restart Your Mac
Rebooting refreshes system resources and can fix temporary freezes.

3. Check Internet Connection
Make sure your network is stable since loading email content depends on connectivity.

4. Clear Browser Cache (if using browser)
Sometimes cached data interferes with loading new content.
- For Safari: Go to Safari menu > Preferences > Privacy > Manage Website Data… > Remove All.
- For other browsers, clearing cache is under their respective settings.

5. Update Software
While OS X 10.15.7 is your current system, ensure your Mail.com app or browser is updated.

If after these steps the problem persists, the issue might be related to account synchronization or corrupted emails on the server side, which might require removing and re-adding your email account or reaching out for deeper support.

Could you please let me know which of these steps you've tried so far? Also, if you are using the app, can you confirm its version? That will help me provide more specific guidance.