I agree with forcing people to use the wiki. At my school, the email system was getting overwhelmed with mass emails from students selling stuff, looking for rides, trying to find items. There was already a site created by a student to sell things, look for rides, and post lost items, but nobody used it. Now they have just cut off access to mass email for nearly everyone, and the adoption of the site has gone up somewhat. So I would suggest that you first start with managers, trying to get them to only accept some things from the wiki, and consider cutting off some mass email access if it is being used for things that you want to move to the wiki. You will upset some people, but you will get them using the wiki.