To me it still looks like you have not configured your e-mail server correctly. But if you verified that the standard Joomla contact form works than you might be right to look somewhere else.
Anyway, the e-mail is send from a function sendEmailNotification in the file components/com_facileforms/facileforms.process.php.
TheMuffinMan is the one that can validate my previous statement because he knows the code much better.
Joomla 1.5.18 | BreezingForms 1.7.1 build 728 | Eclipse 3.4.2 | Subversion 1.6.2 | Apache 2.2.11