We are aware of issues some users are having with logging into Yahoo accounts and are working to fix this as quickly as possible.

Will blocked contacts know I have blocked them?

When you add an email address to your blocked email addresses list there is no notification sent to the blocked email address in question.

Whenever your blocked contacts send you a message, they will not receive a failure notice confirming their message was not delivered. Since the email in question will never arrive to your inbox, you will not know they have sent you a message.