Applies to: Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2007-07-16

This topic provides information about how to troubleshoot the mail flow problem in which you cannot send messages from a Microsoft Exchange Server 2007 Hub Transport server to a remote destination. This problem occurs when you try to send e-mail to an external domain and the message is put in the Unreachable queue on the Hub Transport server. The last error for the message says "A matching connector cannot be found to route the external recipient."

The Unreachable queue is a persistent queue that contains messages that cannot be routed to their destinations. Regardless of destination, all messages that have unreachable recipients reside in this queue. The messages remain in the Unreachable queue until they expire or until the administrator resubmits the messages to the categorizer. For more information about how to resubmit messages in the Unreachable queue, see How to Resubmit Messages in Queues.

Unlike earlier versions of Microsoft Exchange, mail flow to and from the Internet is not enabled automatically when you install Exchange 2007. You must configure an Edge Subscription or manually configure Send connectors to enable Internet mail flow. For more information, see the "For More Information" section of this topic.

Configuring Internet Mail Flow

To complete mail flow configuration for the Exchange organization and to send and receive e-mail to and from the Internet, you must configure Send connectors and Receive connectors that enable at least one Hub Transport server to connect to the Internet. You can configure Internet connectivity for a Hub Transport by using any of the following methods:

  • You can deploy an Edge Transport server and subscribe it to the Exchange organization. This is the recommended deployment method. By default, when you create the Edge Subscription, the required Send connectors are automatically created. You do not have to modify the configuration of the default Receive connector on the Hub Transport server for this scenario.

  • You can send and receive Internet e-mail by relaying through Microsoft Exchange Hosted Services or another third-party Simple Mail Transfer Protocol (SMTP) gateway server. In this scenario, you have to create a Send connector and a Receive connector between the Hub Transport server and the external SMTP servers that process and route Internet e-mail.

  • You can establish Internet mail flow directly through a Hub Transport server. In this scenario, you have to create a Send connector that routes e-mail to the Internet. Also, you have to modify the configuration of the default Receive connector to accept anonymous e-mail submissions. In this scenario, the Exchange 2007 Hub Transport server can be reached directly through the Internet. We don't recommend this topology because it increases security risks by exposing to the Internet the Exchange 2007 server and all roles installed on that server. We recommend that you implement a perimeter network-based SMTP gateway, such as the Edge Transport server, instead.

For More Information