XFOR: IMC NDRs or Misdirects Mail Without Domain Address

• Microsoft Exchange Server, version 4.0

SYMPTOMS

The Internet Mail Connector (IMC) may return outbound mail as undeliverable, giving the reason "Host Unreachable," or it may misdirect mail to an incorrect SMTP host.

CAUSE

If the SMTP recipient address does not include the "@domain" part of an address, the IMC attempts to resolve a domain name consisting simply of the period (.). If the Domain Name Service (DNS) queries for the domain "." result in an answer, the mail is sent to that SMTP host. The message will eventually be rejected by the receiving host, because the user name does not exist on that erroneous SMTP host. If the DNS queries for domain "." do not result in an answer, the message is re-queued by the IMC for possible delivery later with the reason "Host Unreachable".

WORKAROUND

To work around this problem:

• On the Connections property page, configure the IMC to deliver all mail to a specific host that is able deliver mail without the domain part of the address.

STATUS

Microsoft has confirmed this to be a problem in Exchange Server version 4.0. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.