My iCloud email stopped syncing with Outlook on my Windows PC. I can still access it through icloud.com in the browser.
Apple changed their authentication requirements for iCloud email on Windows. You now need to use an app-specific password instead of your regular Apple ID password. Go to appleid.apple.com, sign in, go to Sign-In and Security, then App-Specific Passwords. Click Generate an App-Specific Password, name it Outlook, and copy the generated password. In Outlook, go to File, Account Settings, select your iCloud email account, and change the password to the app-specific password you just generated. Make sure two-factor authentication is enabled on your Apple ID (it is required for app-specific passwords). If Outlook still does not sync, try removing the iCloud account from Outlook entirely and re-adding it. When adding, use the IMAP settings manually: incoming server imap.mail.me.com port 993 SSL, outgoing server smtp.mail.me.com port 587 TLS/STARTTLS. Use your full iCloud email address as the username and the app-specific password as the password. If you have iCloud for Windows installed, make sure it is updated to the latest version — older versions have known sync issues with newer Outlook builds.
