try out a new 'new-mail-alert' icon for mail alerts. I believe this icon came from arvind.

mail/base/jar.mn

@@ -24,6 +24,8 @@ classic.jar:
 +   skin/classic/messenger/threadPane.css           (skin/threadPane.css)
 +   skin/classic/messenger/messageHeader.css        (skin/messageHeader.css)
 +   skin/classic/messenger/mailWindow1.css          (skin/mailWindow1.css)
++   skin/classic/messenger/icons/new-mail-alert.png (skin/icons/new-mail-alert.png)
++   skin/classic/communicator/alerts/alert.css      (skin/alert.css)
 
 comm.jar:
 +   content/navigator/viewSource.xul                (content/viewSource.xul)

mail/base/skin/alert.css

@@ -0,0 +1,76 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: NPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.1 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is mozilla.org code.
+ *
+ * The Initial Developer of the Original Code is 
+ * Netscape Communications Corporation.
+ * Portions created by the Initial Developer are Copyright (C) 1998
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *  Scott MacGregor <mscott@netscape.com>
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or 
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the NPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the NPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+/* ===== alert.css =====================================================
+  == Styles specific to the alerts dialog.
+  ======================================================================= */
+
+@import url("chrome://global/skin/");
+
+@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
+
+.alertBox {
+  background-color: moz-Dialog;
+  min-height: 50px;
+  border-right: 3px solid #7B969C;
+  border-bottom: 3px solid #7B969C;
+  border-left: 3px solid #7B969C;
+  border-top: 3px solid #7B969C;
+}
+
+.alertImageBox {
+  margin-left: 4px;
+  margin-right: 6px;
+  min-height: 46px;
+}
+
+.alertTitle {
+  font-weight: bold;
+}
+
+.alertText {
+  margin-right: 6px;
+}
+
+.alertText[clickable="true"] {
+  cursor: pointer;
+  color: #1455D6;
+}
+
+.alertText[clickable="true"]:hover:active {
+  color: #424F63;
+}