Recently I dealt with a customer email problem involving the above error message, and we both agreed it'd be a good idea to post the solution online for the benefit of others.
If you're using Outlook 2007 on MS Windows 8 and also receiving the error message in a pop-up looking something like this image, then please follow the steps below to see if that resolves your problem:
Outlook 7 Error Message: "The server you are connected to, is using a certificate that cannot be verified. The target principal name is incorrect".
This will occur if you are using an old version Microsoft Outlook that has not had the latest updates installed.
For example - if you load Outlook 7 onto a Windows 8.1 computer, the error above my appear.
Usually, the Windows Update on your computer, will automatically check and install Windows Updates. But for Outlook Updates, you need to configure your Windows Update settings, so that it also updates Microsoft products on your computer (e.g. Outlook 7).
To do this in Windows 8.1, you can use the instructions below:
1. Open the Windows 8.1 Search box by clicking the small magnifying glass icon top right of screen.
2. Type in 'Windows update settings' and select it when it appears.
3. Click 'Choose how updates get installed'
4. Put a tick in the box alongside 'Give me updates for other Microsoft Products when I update Windows'.
5. Click the Apply button.
6. Close the screen (press Alt F4).
7. Open the Windows 8.1 Search box by clicking the magnifying glass icon top right of screen.
8. Type in 'Windows update' and select it when it appears.
9. Select 'Check for updates'.
10. Click 'Install'.
11. Restart your computer when prompted.