A relative asked me this because access to Yahoo! Mail is disabled at work. I suggested that signing up Yahoo! Plus for $20/year to have POP3/SMTP access, then use Gmail or Outlook to access Yahoo!. However Gmail is also disabled. I was wondering if there is any workaround.
The last option would be to purchase an iPhone or Android smart phone and access his Yahoo! Mail via the wireless network.
I'm testing Threadsy and it looks really promising, even as a general purpose web email aggregator.