Re: trying to sync Yahoo! Mail email on Nokia Lumina 520, get error message 8007274C, why?
If you're email won't sync, this is the general troubleshooting procedure I go through:
1 - Reboot the phone
2 - Log into your email on the web. If you are already signed in with your browser, sign out and try to sign back in. This will tell you if your account has an issue.
3 - Verify that the server settings haven't changed, in other words, check your POP3 and SMTP settings with your email provider.
4 - Delete the account from your phone and re-add it.
See if any of these things fix your problem. Good luck, and feel free to ask any followup questions if you have any other errors.