How to manage bandwidth for Cached Exchange Mode

To start: yes it is going to completely kill your inter-site performance. Outlook/Exchange is not smart enough to limit the traffic, you will need to configure QOS if you plan to do this during business hours. As far as re-downloading the mailbox when a user gets a new PC: this is also something that will have to happen with cached Exchange mode. When you configure Outlook's connection to your Exchange server it has to create a new local .OST file (local cached mailbox). A quick search of Google shows there are ways to create the .OST file, stop the download, and replace the new .OST with an old .OST file of the same name. However I have never tried this and cannot condone it. I recently consolidated users in my company onto one domain and had to deal with the re-download of the local .OST file (very Frustrating).

A side note: Although Outlook 2003/2007 allows up to 20GB .PST(http://support.microsoft.com/kb/830336/en-us), I HIGHLY recommend you keep them no higher than 1.5 Gigs anything over that will cause problems. The problems are a mixture too, sometimes outlook will fail to start, sometime it’ll stop sending and receiving, sometimes it will randomly delete mail, other times the entire file can get corrupted. It took me a while to narrow down what was wrong with some of my users Outlook, after talking to another Sysadmin who experienced the same problems I found out it was over-sized PST's. I just want to save you some headaches a year or two down the line.