Probably a temporary issue, and area dependent. E.g. yesterday there was an outage in my area.
Remember these forums are peer to peer, To help you here would you have to post some additional information (Probaly not posting your actual id and definetly not showing your password). Need things like your general area and server settings you use. The server in most cases is smtp.verizon.net port 465 SSL/TLS , password required, Normal(clear text) passwword. Also what app you are using (apple IOS, Android, Thunderbird, Windows 10 Mail, etc)
I suddenly had the same issue using my Verizon.yahoo email via Outlook. Tried re-entering my settings and finally found that if I uncheck the "Require logon using Secure Password Authentication (SPA)" checkbox, the email (incoming and outgoing) started working again. Good luck!