Customize message that is delivered by smtp security server when mail is blocked

[lopaten]

Does anyone know if you can customize this message that is returned by the firewall when the smtp security server rejects mail?

Here is the text of the email sent by the firewall when an email is rejected:

-----Original Message-----
From: postmaster@fwngx26.test.ca [mailto:postmaster@fwngx26.test.ca]
Sent: Wednesday, June 25, 2008 12:20 PM
Subject: Undeliverable mail
Your mail message could not be delivered, or may have encountered some trouble in the delivery process.
Due to security reasons the body of your undeliverable mail will not be attached.
Final error mail: mail can not be delivered to the following recipients :
<test@test.ca>