Well I have not ever researched this subject of sending Japanese via email really before, I cannot essentially answer your question. I can, however, point you in the direction of your new friend (since you seem like a new user here at the Monastery,)super_search!
in reply to cgi email Japanese contents scripting problem
I typed in a search for this type of question, and came up with a topic that was asked in the past that might help a little bit on this topic, it was Pyuuta: Programming in Japanese.
If I were you, I would search on the topic of Perl and Unicode programming. This might help you to figure out how to achieve what you are asking.
Hope this helps you somewhat ...