diff -up squirrelmail-webmail-1.4.22/class/mime/Message.class.php.php54fixes squirrelmail-webmail-1.4.22/class/mime/Message.class.php
--- squirrelmail-webmail-1.4.22/class/mime/Message.class.php.php54fixes	2012-02-24 13:47:04.997225305 +0100
+++ squirrelmail-webmail-1.4.22/class/mime/Message.class.php	2012-02-24 13:47:05.031224597 +0100
@@ -359,6 +359,7 @@ class Message {
                         case 0:
                             if (!isset($msg)) {
                                 $msg = new Message();
+                                $msg->header = new MessageHeader();
                                 $hdr = new MessageHeader();
                                 $hdr->type0 = 'text';
                                 $hdr->type1 = 'plain';