Hello everyone,
Today I've received a call from one of our client's main office in Luxemburg, telling me that the 4000 people using Microsoft Outlook were having some 'difficulties' working with it!
It happens that, after some analysis, most of the MSCRM users Outlook clients were making 20000 requests in one second (yes: 20000rq/s 
) on the Exchange servers (which are in cluster!)... and the Exchange servers could not cope anymore with the additional workload.
Anyway, they called Microsoft and an engineer worked out the solution for them: the KB #916566
KB916566
I recommend using either method 1 since I think that auto-tagging is a useful feature (but method 2 might be helpful as well... anyone having to say something about it?).
A test on the 4 'out of the top 10 most request makers' users with method 3 proved to be efficient (they were not in the 'top 10' anymore 
) so it's up to your infrastructure team to test on a small group of users before going into production!
Olivier