I forget the defaults for 5.2. Out of the box it should work, I think. The clients can use TLS/SSL if they wish and you've installed CERTs, etc., but should not be required.
Again I do not have a copy of a default iMS 5.2 imta.cnf file in front of me. Look for keywords starting with 'musttls'.
From a security point of view this is a bad idea...
-Chad-