http://blogs.msdn.com/stephen_griffin/archive/2009/06/17/named-properties-in-exchange-2007-sp2-and-beyond.aspxWith the recent Rollup 8 for Service Pack 1, the Exchange team previewed a change designed to reduce the impact of inbound SMTP messages on the named property map for a store. Jason talked about it here . The gist of the change is that before, randomen-USCommunityServer 2.1 SP1 (Build: 61025.2)