Maybe something along the lines of Mail::OnTheFly or Mail::AdHoc because that's what seems most different about these modules - they allow you to do things like create lists and users on-the-fly rather than as permanent parts of your mail setup.

I like Mail::Application, Mail::Action, Mail::RPC but they don't seem to capture the fact that it's directives in the email itself which initiate the Actions. Maybe something like Mail::Message2Action or Mail::CommandLang. (Well those kinda suck, but provide more explicit explanation and could encompass many other sorts of modules)