Administering some Exchange servers the last few years, I've always wondered why Microsoft doesn't feature a 'catchall' option or function in Exchange.
Sure, it's a magnet for spam, but knowing so, I am more than happy to use it still.
Playing around with Exchange 2007, I tried searching for this functionality again. And in Exchange 2007, again no built in option for this. But there is a solution. Reading http://forums.microsoft.com/TechNet/ShowPost.aspx?PostID=1346329&SiteID=17 , there is an option which is also described in a Technet article (I have trouble providing a link, unfortunately). But reading the forum post, it seems it needs an edge server (thus requiring at least two exchange servers) and you also need to specify an exclusion list for all existing accounts.. :-(
But reading the forum post I also checked out the catchall agent provided by a Microsoft Employee (Wilbert). Reading through the documentation doesn't mention whether it will overcome the previously mentioned issues (requiring a multiple server Exchange install and manually adding exceptions for existing recipients). The author wasn't sure and adviced me to test.
So I did and I am now a happy person running a single exchange server install with a catcall account which receives all mail for my domains for which no specific recipient/mailbox exists. So if you need catchall functionality for your Exchange 2007 environment: check out http://www.codeplex.com/catchallagent.