I'm using a Sky email account (Sky use Yahoo to manage their email services), and I use the Samsung email client.
Recently, Sky moved from using a recognisable password when you connect via an app or Outlook to an 'app password', which is more secure. I'm pretty sure that the 'normal' password still works on a web browser.
This may not apply to bonafide Yahoo accounts, but if it's Sky Yahoo, check out the Sky help pages and search for 'app password'. I think I also manually added the Sky email account rather than selecting the wizard option for Yahoo. Again, configuration options for this are available on the Sky help page.
Hope this helps.