Q: We were able to do the rebasing of appts, but now historical appointments in 1999 are incorrect. What effect does the rebasing tool have on old messages that are restored from archive systems like the vault. What about items that are restored on Exchange? What shoudl we know about appointments that occur in prior years during the 3 week offset... will the times on old emails be 1 hour off?
A: Are you saying appointments going back in time are off and appointments in the DST 2007 time are ok? This expected. Historical time will be changed by 1 hrs in the DST Window.
With respect to Outlook, anything that is stored in UTC (e.g. message delivery times) will be converted to local time using the current time zone rules. This means that looking backwards in time at received messages (whether restored from backup or not) will report incorrect local times for items in the DST delta periods. The UTC times are always correct (and, I would imagine, what can/should be used in sort of legal/compliance situation).