Yahoo blocks mail addresses if you are spamming or abusing their ToU. You should have been sent an email explaining why you are blocked from sending emails and who to contact to appeal.
By going to yahoo and setting an acount or check your mail.
Are you a Yahoo user facing the unexpected issue of Yahoo Mail not sending but receiving mail? Here are some steps that you can follow to troubleshoot it: Check for any typos in the recipient's email address in your email's "To" field. See that the email is not in your drafts. This indicates that your email has not yet been sent. Check that your email is not being redirected by filters or blocked by the recipient’s spam or blocked address list. If you use Yahoo Mail on your mobile devices, sign off and then log back into the Yahoo Mail app. Reinstall it if the issue is still not resolved. If you get a security verification while sending, then you must try sending a test mail using the desktop version of Yahoo Mail. Identify the problem as early as possible; it can be due to the sender's or receiver’s end. Try these fixes to resolve the issue.
Yahoo mail
Yes, you can access your yahoo mail normally on the PC after it has been blocked from the app.
Yahoo mail can be checked in the official Yahoo site and not in any other site.
Log into yahoo and click "check mail." There should be an inbox with new messages in it.
I am blocked on everything to repair the e-mail repair what now?
The easiest way to check ones Yahoo mail is to log on to the Yahoo website via either a computer, laptop or smartphone. Once at the site simply click on the mail icon and log in.
MSN
See help.yahoo.com/l/uk/yahoo/mail/yahoomail/context/context-05.html for details
CHECK