I use the following code to display an error message if there are problems while sending messages through my SMTP server:

PHP Code:
if (PEAR::isError($mail)) {

$errorMessage $mail->getMessage();
print (

Today I put a bogus address on my domain to see what would happen. I used xyz@mydomain.com. Here is the error I got:

Failed to add recipient: xyz@mydomain.com [SMTP: Invalid response code received from server (code: 550, response: No Such User Here")]

I tried sending the same test message to a bogus account on another domain. I tried using xyz24601@verizon.com and the message actually went out successfully and later bounced about 5 minutes later. So why does the "No Such User Here" message only work on my own domain? If I can figure out how to do this for other domains, then I can write some code that will suspend a user's account that is generating send errors on the fly.