What SMTP are you using? Is it your server? or are you ussing a server of your internet provider for example?
Is the FROM address you're using in the software is allowed to send out e-mails using that server?
If you know how to check that SMTP thru the telnet command in the command prompt you can check it with that 'from' address and see what exacly is the problem,
if not, you can send us the SMTP details (to
support@inwise.com, and not here of course) and we can check it for you.