There are a number of reasons you might experience difficulties with POP access.

Password
Are you sure that the password you're using to retrieve your Yahoo! Business email is correct?

To check, go to http://mail.yourdomain.com (replace yourdomain.com with your own domain). If you are able to sign in to your Yahoo! Business Email account with the password you have been using, then the password is correct. If you can't sign in, you can request a new password by filling out the password request form.

Forwarding
Have you selected the forwarding option in the Yahoo! Business Email "POP & Forwarding" options? If so, you won't be able to use POP, as POP and forwarding are separate features that can't be used at the same time. Learn more.

Client Settings
Is there a problem with the email client settings?

Here are the basic server settings for Yahoo! Business Email:

For more information, see your client's POP configuration settings.

Setup
Did you select an incompatible sign-in method or server type when you set up your email client? To check your settings, please review your client's POP configuration settings.