That means that the site already set the encoding to SJIS which got you the mojibake. It was supposed to be EUC("
looks like broken EUC") so you need to set the encoding to that.
I saved what you have to notepad and viewed it in mozilla firefox setting the encoding to EUC and got this
some characters were still messed up)
ナ?CテェC窶鼎窶呂あEあ 窶笛窶堙溪?堙??堋ュあE窶慊「ツ?「テ・ツ「あ窶敖「ニ椎クあ ナスナク窶堙坂?堙懌?堋ス窶「テ岩?堙娯?堙?窶堙娯?堙ー窶ーテウ窶堋オ窶堙懌?堋キツ。ナ?y窶堋オ窶堙昶?堙俄?堋オ窶堙??堋「窶堙??堋ュ窶堋セ窶堋ウ 窶堋「ツ。 PSP窶堙ー窶ーテウ窶堋オ窶堋ス窶慊ョ窶ーテヲ窶堙債、ナス窶樞?堙固スg窶堙≫?堙??堋「あE窶ケ@ナスツ」ヒ愬クナスツ「あツ?」あナスD ツ垢窶殿邃「C窶楪「テ・CあEツ最クああああE窶凖「ナス~窶堋キあEあ窶鼎窶「ツ「窶僂窶慊「ナ辰ナクツ「窶僂ツ拭あ ニ探ツーニ弛ツー窶堋ェ窶堋?あEヒ愬クツ?「ツ?「窶板」テ?ナクナスツ」ナ。@ナスツ「テゥツーツ申テ、ツ「あ窶抔ああナ辰ツ燭あ 窶堙?スv窶堙≫?堙??堋「あE
That makes a lot more sense even with the extra stuff and I think that when using yahoo mail, if you set the encoding to EUC-JP or Japanese(EUC) or whatever they call it in your browser then it will come up correctly. SJIS and EUC are both standards that you need to try. Some sites will use Unicode too. Especially if it has characters other than japanese/chinese/korean. Try every encoding until it looks right.