Dynamic Senders

Hello, I have a working form running app to sand box, I am now trying to make the sender dynamic. When I send the form with the sender email that was set up with original sand box account everything works fine. But if I try to use the second sender, the form never shows up in the inbox, and I get no error message. If would be great if the sandbox would log errors some place to trouble shoot these kind of issues when developing. I have confirmed the second senders email. What is going wrong? What is the best way to handle multiple senders? Thanks, Todd