In the default modus operandi, Outlook 2007 likes to be in cached mode when running against Exchange, which is generally a *good thing*. Cached mode means there are (by and large) fewer occasions to go back & forth to the server, as it operates by synchronizing a local copy of the mailbox down to the OST file on the client. This means that operations such as content indexing (which Outlook now does by default), sorting, filtering etc, all happen on the client rather than hammering the server.
Outlook 2003 did this too, but 2007 offers a new capability in caching the calendars of other users on your behalf. Now that's generally a good thing too - it means that when you open someone's calendar in Outlook, it adds that user's calendar to your cache so that you can see it when offline, and if it's someone you regularly snoop on (let's face it, a lot of calendar lookups are just checking what people are up to, aren't they?), then it will be quicker in opening the calendar in future, since Outlook doesn't have to go back to the server for everything.
A possible downside to this is if you're in a large organization and you routinely (but occasionally) open lots of people's calendars - what then happens is that Outlook spends time and increases the size of your OST by dragging everything down to your PC.
There are a couple of options to mitigate this potentially unwanted behaviour:
- Remove unwanted calendars from your list. If you go into the Calendar in Outlook, you might see a large list of "People's Calendars", meaning you've viewed them before. You could right-click on each individual calendar on the list and choose "Remove ..." and it will ditch that item from your list and also stop synchronizing it (assuming you want to continue synching some other calendars), or...
- Go to Tools | Account Settings | double-click on <Exchange Server account> | More Settings | Advanced and clear the check-box which says "Download shared folders..."
If you're experiencing problems with excessive calendar synch traffic, one of these options might sort you out...