You can't access YahooMail on your DXG?
There is a mobile version of YahooMail at:
http://m.yahoo.com/mail
Why don't you use that?
btw, I got that link from Kinstant (
http://www.kinstant.com ), which has quite a number of links to mobile versions of websites, including fields in which you can Kindle-friendly-ize whatever site you want.
It even works with Google News (I just put news.google.com in one of the custom fields and it worked fine.)