I'd like to suggest you ask this question in Exchange forum: http://social.technet.microsoft.com/forums/en-US/category/exchangeserver/
TechNet Community Support
Try bringing up ADSIEdit and look at the attribute whenChanged. This is a freeware tool from Microsoft.
MVP - Directory Services
MCITP: Enterprise Administrator
MCTS, MCT, MCSE, MCSA, Security+, BS CSci
2008, Vista, 2003, 2000 (Early Achiever), NT4
http://blogs.dirteam.com/blogs/paulbergson Twitter @pbbergs
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