You can test rewrite rules with the imta test -rewrite command. The -noimage qualifier will allow you to test changes made to the configuration file prior to recompiling and reinstalling the new configuration.
You may find it helpful to rewrite a few addresses using this utility with the -debug qualifier. This will show you step by step how the address is rewritten. For instance, try issuing the command:
% imta test -rewrite joe@alpha.com
and see what happens. For a detailed description of the imta test -rewrite utility, refer to Chapter 2, "Commands Reference."