Sun Java System Messaging Server 6.3 Administration Guide

26.4.5 Illegal Host/Domain Errors

You may see this error when an address is provided to the MTA through a browser. Or, the error may be deferred and returned as part of an error return mail message. In both cases, this error message indicates that the MTA is not able to deliver mail to the specified host. To determine why the mail is not being sent to the specified host, you should follow these troubleshooting procedures: