https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=196017
The latest squirrelmail did not convert convert Subject to "zen-kaku
kata-kana". Usually, if a user used "han-kaku kata-kana" in the body
or header, any mail application would convert it to "zen-kaku kata-kana".
The squirrelmail also should convert.

diff -up squirrelmail-1.4.18/functions/i18n.php.zenkaku squirrelmail-1.4.18/functions/i18n.php
--- squirrelmail-1.4.18/functions/i18n.php.zenkaku	2009-05-07 23:55:44.000000000 +0200
+++ squirrelmail-1.4.18/functions/i18n.php	2009-05-12 09:24:06.063892916 +0200
@@ -625,6 +625,7 @@ function japanese_charset_xtra() {
                 $ret = encodeHeaderBase64(mb_convert_encoding($ret,'ISO-2022-JP','EUC-JP'),
                                           'iso-2022-jp');
             }
+	    $ret = mb_convert_kana($ret, "KV");
             /**
              * if text is in ascii, we leave it unchanged. If some ASCII
              * chars must be encoded, add code here in else statement.