Yahoo mail and proxies

I am trying like hell to find proxies that work with yahoo mail and am unable to get any to work. I have tried web proxies, scrapes http, https, sock 4 and 5, as well as those supplied by 4 different elite (so called) companies, and nothing.

Has anyone found something that works?

All I want to do is verify about 500 accounts and use them to sign up for another site, but am unable to get in in any fashion.

Has anyone else had similar problems?

No, This is so strange, I didn't face any problem like this till now.

I think it was because of the quality of your proxies. I have no problem creating yahoo accounts with my proxies (private of course). The only thing is that yahoo randomly puts captchas, so you might need a captcha solver service.