IPC::System::Simple doesn't have a mailing list. It has an official support forum, and you've just found it.
If you have any questions, want to start a discussion, or have suggestions for improvements, here's the place to put them.
Bugs and patches should be reported to the bugtracker. Please try to ensure you're using the most recent module version if you're reporting a bug, and please try to check if the bug has already been filed so we don't end up with bugs being reported twice.
All the best,