Yes, as said above sending email in Japanese usually means sending the the text (7-bit) jis-encoded.

(1) Before you can do this you need to find out it which encoding your programm receives the data.This could be jis, shift-jis, euc-jp or Unicode. You can find out the encoding with the Jcode module from CPAN:

 
use Jcode;
my $encoding = getcode($content);
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(2) After you have found out the encoding you want to convert your string to 7 bit jis.

my $mailtext = Jcode::convert($content, "jis", $encoding);
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Appart from that, the Jcode module also supplies some basic MIME handling functions.
Hope that helps,

Hanamaki