Pay for it so you actually do get access to their POP3 and SMTP servers. If
it is a paid account, Yahoo doesn't have any tech support for the service
for which you are paying them? Did you read their online help web pages?
If it is a freebie account, you have to use their webmail interface, or use
YahooPOPs which runs as a local HTTP-to-POP3 protocol converter proxy.