XADM: Unable to Send to Remote Users Using SMTP Addresses

• Microsoft Exchange Server, version 4.0

SYMPTOMS

One of the following errors may be written to the Event Viewer Application Log by the receiving MSExchangeMTA when a message is sent between Exchange Sites using the SMTP Address of an Exchange user, rather than the X400/X500 Address:

  Event ID 142: "Unable to route to c=us;a=
  ;p=SendingOrgName;o=SendingSitename;DDA:SMTP=user1@RecvOrg.RecvSite.com."

   Event ID 290: "A non-delivery report (reason code unable to transfer
   and diagnostic code MTS-congestion) is being generated for message
   c=us;a= ;p=orgname;l=RecvMTAname-960808200654z1. It was originally
   destined for
   c=us;a=;p=orgname;o=SendSite;DDA:SMTP=alias@RecvSite.orgname.com; and
   was to be redirected to.[MTA DISP:RESULT 20 136]."

    - "Recipient name not found",

    - "due to congestion in the message transfer service".

CAUSE

This error condition is caused by the receiving Exchange MTA's inability to route a message addressed with an SMTP address to an Internet Mail Connector for further resolution. This behavior is by design.

WORKAROUND

There are three methods to workaround this problem, depending on whether there is replication between the sites.

1. Whether replication has occurred or not, using the X400 Address instead of the SMTP address to send to users in other sites will work, because Exchange is a native X400 messaging system.

2. If replication has occurred between the sites and an IMC is available, the IMC can be configured (using the Email Domain . . . button on the Connections tab) to route all mail addressed to the various Exchange SMTP addresses (the SMTP addresses of users that actually have a mailbox on the Exchange system) will be forwarded directly back to the Exchange Server. In this case, the Address Space on the IMC should be SMTP and left blank. Once the message goes out the Internet Mail Connector and comes back in, it will be matched to an address in the Exchange directory and will be routed to the appropriate mailbox.

3. If replication has not occurred among the sites, then an IMC must be configured in each site with the Address Space configured as "*@localsite.organization.com", for example. The IMC must be configured, as in the second case, to forward all mail back to the Exchange Server itself.

MORE INFORMATION

Exchange Server is not designed to support messaging between Exchange users on different sites using the Internet-style, or SMTP, addresses. Each time a message is sent that is addressed with an SMTP address, the MTA looks for a valid route for that recipient in the Routing Table (that is, the Gateway Address Routing Table, or GWART). If a route is found to another site through one of the site connectors (Site Connector, Dynamic RAS Connector, or X400 Connector), the MTA will successfully hand off that message to the MTA in the other site. However, if the receiving MTA cannot find another valid SMTP address space in its GWART to forward that message to, then it will generate this error condition.