Where is the actual sending done?

Where in the module is the actual sending of nodes invoked? I'm trying to use this module to send multiple nodes but currently I can't even send one. I'm not getting any error messages or any errors in the Drupal or server logs so obviously something is going wrong in the code (perhaps an invalid interaction with another module) but I can't determine where to start looking.

I'd like to start with the code that sends the email and work backwards from there. I just need to be pointed to where that is.