--- a/mail/base/content/msgHdrViewOverlay.js
+++ b/mail/base/content/msgHdrViewOverlay.js
@@ -2520,17 +2520,17 @@ function nsDummyMsgHeader()
 {
 }
 
 nsDummyMsgHeader.prototype =
 {
   mProperties : new Array,
   getStringProperty : function(aProperty) {
     if (aProperty in this.mProperties)
-      return this.mProperties[property];
+      return this.mProperties[aProperty];
     return "";
   },
   setStringProperty : function(aProperty, aVal) {
     this.mProperties[aProperty] = aVal;
   },
   getUint32Property : function(aProperty) {
     if (aProperty in this.mProperties)
       return parseInt(this.mProperties[aProperty]);