In the log you are probably seeing Send e-mail for bucket xyz...Ask your SMTP server administrator for the log and take a look at that.
In order to test I would try SMTP4Dev. It is a dummy SMTP server that runs on Windows 7/Vista/XP/2003/2010. It will not actually send out e-mails but will receive them so you can test if NPrinting 17 is sending them out.
HTH - Daniel.