I've you haven't seen this before Gavin Smyth from Microsoft Research put together this cool VSTO plugin to allow you to send an Email from Outlook that will disable the Reply, ReplyAll and Forward Buttons on the Outlook ribbon http://research.microsoft.com/en-us/projects/researchdesktop/noreplyall.aspx and the how to posts about the VSTO http://blogs.msdn.com/b/gsmyth/archive/2011/09/18/noreply-vsto-add-in-wrap-up.aspx . Note this only works in Outlook (not OWA or ActiveSync etc) but basically what a users would see when they receive a message is How this works is it sets the PidLidVerbStream Property on a message which is mostly documented in the http://msdn.microsoft.com/en-us/library/ee218541(v=exchg.80).aspx protocol document. I say mostly because the format you get when using the methods from the NoReply Addin is a little different from the format documented which is for Voting buttons but its good enough to work with. The Verbs that this...
Pushing the Envelope in Messaging and Office 365 Development