How to change encoding temporarily?

[ssSslang]

Hi there!

I use Gnus with utf-8 encoding. Now I find the suck microsoft hotmail
webmail can't decode my mail correctly. So I must change to another
encoding(gbk) when sending mail to those who use hotmail mail box.

Everytime I just write in my buffer with:

(setq mm-coding-system-priorities '(iso-8859-1 gbk utf-8))

eval it, send mail, and then roll back. I thought of binding these two
functions to some keys. But I often forget to do these before sending
mail. Is it a hook related to mail address can be use for sending mail?

-- 
ssSslang