Problem:
I get this sort of error when I try to send from my phpBB2 install from Fantastico. Failed sending email :: PHP :: DEBUG MODE Line : 234 File : emailer.php
Solution:
The most common cause is that you are either sending to or sending from an invalid email address.
You will want to create a new email address, and change your profile to use a different Email address.
Log in, and click Profile at the top of the page.
You will also want to change the email address emails are coming from.
To do this, log into the Administrator Index, and click on the link under "General Admin" called "Configuration".
Scroll all the way down to the bottom, and change the email address there as well.
You should no longer get the php error.
To further test that php mail is working for a specific email address, a script like this should send an email to example@Most Host.com with the Subject line of "test" and body of "test".
<?
mail("example@Most Host.com","test","test");
?>