Please see if you can follow these instructions. They should help solve the "Not synced yet" error you see on your computer.
1. Exit the Mail app
2. Click on the Windows Start button located in the bottom left corner, and then click on Settings
3. When the Settings window opens, click on the Privacy section
4. When the Privacy window opens, click on Email on the left
5. Make sure the access is set to On (both on the top and on the bottom)
6. Now click on Calendar on the left
7. Make sure the access is set to On (both on the top and on the bottom)
8. Close the Settings window
9. Start the Mail app
10. Check if it will automatically sync the e-mails. If not, you can click on the refresh icon in the upper right corner (2 curved arrows). In case it still won't sync, please restart the computer and check again
Let me know if these instructions helped solve the problem.