1) Make sure the from address is a valid address on your websites domain
2) Make sure you are not setting the from address and to address to the be the same.
3) Double check that you are entering the correct SMTP Server in the mail settings section.
4) In the mail settings section, you may need to check the option to "Include the From address as an extra parameter"
are you setting the email behavior to redirect to another page after the email is sent? If so, does the redirect occur correctly?
Who is your host?
can you send a copy of your page in a zip archive along with the webassist/email folder so I can examine the code?