Email sent from the site to users outside your domain, or all email sent from the site is not arriving. When following the instructions from the FAQ on ColdFusion Mail Troubleshooting you see the "Error 550 5.7.1 Unable to Relay" errors in your Coldfusion Mail.log.
Unable to relay errors are generally the results of policies on your email server which prohibit the web server from relaying messages correctly. The outlined steps below will help you configure an exception for allowed relaying in Exchange 2000/2003.
Error messages in the Mail.log will appear similar to the following:
Invalid Addresses; nested exception is: class javax.mail.SendFailedException: 550 5.7.1 Unable to relay for firstname.lastname@example.org
Relaying configuration is available from the Exchange System Manager under the SMTP Virtual Server properties at:
<Organization> | Servers | <Server> | Protocols | SMTP
Open the virtual server properties and select the Access property page:
Next click the Relay button:
As the dialog shows, by default relaying is allowed for the list of explicitly configured hosts (this list is initially empty). Relaying is also allowed for all authenticated connections.
At the Relaying configuration dialog, click on Add:
Add the IP address of the web server. Then 'Ok'. Test sending mail from the site again to confirm you no longer see relaying errors.