We have been testing a Bynari Insight server in our office for the last few weeks. It isn't installed on SME/E-smith, but operates on a server/computer all by it's lonesome. The rest of the network is E-smith based.
The Connector goes on the client machine (i.e. Outlook) to allow it to 'talk' to the Insight server, so I'm not sure whay you would want to put it on the E-smith boxen?
The Insight server works really well. I'm not sure that it is a totally replacement fo Exchange, but it is darned close. It has the functionality that we require.