diff --git a/mailnews/base/resources/content/msgHdrViewOverlay.js b/mailnews/base/resources/content/msgHdrViewOverlay.js
index 045e5f3f6bed..c251e8428770 100644
--- a/mailnews/base/resources/content/msgHdrViewOverlay.js
+++ b/mailnews/base/resources/content/msgHdrViewOverlay.js
@@ -308,6 +308,11 @@ var messageHeaderSink = {
         // for consistancy sake, let's force all header names to be lower case so
         // we don't have to worry about looking for: Cc and CC, etc.
         var lowerCaseHeaderName = headerNames[index].toLowerCase();
+
+        // if we have an x-mailer string, put it in the user-agent slot which we know how to handle
+        // already. 
+        if (lowerCaseHeaderName == "x-mailer")
+          lowerCaseHeaderName = "user-agent";          
         
         var foo = new Object;        
         foo.headerValue = headerValues[index];
diff --git a/mailnews/mime/emitters/src/nsMimeHtmlEmitter.cpp b/mailnews/mime/emitters/src/nsMimeHtmlEmitter.cpp
index 8c77e6b0bc68..3e721edc1f91 100644
--- a/mailnews/mime/emitters/src/nsMimeHtmlEmitter.cpp
+++ b/mailnews/mime/emitters/src/nsMimeHtmlEmitter.cpp
@@ -227,7 +227,8 @@ NS_IMETHODIMP nsMimeHtmlDisplayEmitter::WriteHTMLHeaders()
               nsCRT::strcasecmp("cc", headerInfo->name) && nsCRT::strcasecmp("newsgroups", headerInfo->name) &&
               nsCRT::strcasecmp("bcc", headerInfo->name) && nsCRT::strcasecmp("followup-to", headerInfo->name) &&
               nsCRT::strcasecmp("reply-to", headerInfo->name) && nsCRT::strcasecmp("subject", headerInfo->name) &&
-              nsCRT::strcasecmp("organization", headerInfo->name) && nsCRT::strcasecmp("user-agent", headerInfo->name))
+              nsCRT::strcasecmp("organization", headerInfo->name) && nsCRT::strcasecmp("user-agent", headerInfo->name) &&
+              nsCRT::strcasecmp("x-mailer", headerInfo->name))
                 continue;
         }