Messages that have been replied to by the current Outlook user see the replied message icon instead of the Archive Manager padlock despite the message class being IPM.NOTE.AfterMail. All other stubs do show the AM padlock icon.
As stated at http://support.microsoft.com/kb/291410 “This is a design limitation of Outlook. The forward icon or the reply icon will always be used instead of the custom icon.”
Enhancement Request ST96841 has been issued for this to be considered for a future release of Archive Manager