There is another way of encoding Japanese language to send email without worrying about mb_functions:
Download PHP Jcode from http://www.spencernetwork.org/
and use JcodeConvert function with base64_encode function for the e-mail header and the subject.
$email_to = "[email protected]";
$_POST["name"] = strip_tags(trim($_POST["name"]));
$name = "=?ISO-2022-JP?B?". base64_encode(JcodeConvert($_POST["name"], 2, 3)). "?=";
$_POST["email"] = strip_tags(trim($_POST["email"]));
$_POST["subject"] = strip_tags(trim($_POST["subject"]));
$email_subject = "=?ISO-2022-JP?B?". base64_encode(JcodeConvert($_POST["subject"], 2, 3)). "?=";
$_POST["body"] = strip_tags(trim($_POST["body"]));
$email_header = "From: $name <". $_POST["email"] .">\n";
$email_header .= "Reply-To: ". $_POST["email"] ."\n";
$email_header .= "Content-transfer-encoding: 7bit\n";
$email_header .= "Content-type: text/plain; charset=\"iso-2022-jp\"\n\n";
$email_body = "blah blah blah.\n"
mail($email_to, $email_subject, $email_body, $email_header);