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 -urN squirrelmail-1.4.6.orig/functions/i18n.php squirrelmail-1.4.6/functions/i18n.php
--- squirrelmail-1.4.6.orig/functions/i18n.php	2006-02-10 15:30:31.000000000 -0500
+++ squirrelmail-1.4.6/functions/i18n.php	2006-06-23 15:49:06.000000000 -0400
@@ -487,6 +487,7 @@
             break;
         case 'encodeheader':
             $result = '';
+            $ret = mb_convert_kana($ret, "KV");
             if (strlen($ret) > 0) {
                 $tmpstr = mb_substr($ret, 0, 1);
                 $prevcsize = strlen($tmpstr);