This can be caused for one of two reasons:

1. Path to Sendmail Incorrect
This is the most common reason. Ensure that the path to sendmail is properly entered within your program options. This path is available from your web hosting provider. Also, please note that you must include a -t at the end of the path. Therefore...

/usr/sbin/sendmail

...becomes...

/usr/sbin/sendmail -t

...when entered into the options.2. Duplicate Emails
Another cause may be that the email address entered in the "Company E-Mail" option is the same as the email address on the account you are testing. As a security measure, Sendmail (the built-in linux program used to send emails by AdPass) automatically stops emails from being sent to the address from which you are sending. Try changing your test account's email address to ensure that this isn't the problem.

If the above two solutions don't solve the problem, please contact your web hosting provider, as something may be wrong with web site's mail server.