XCON: X.400 Message Flow in Exchange 2000 (263248)


The information in this article applies to:

  • Microsoft Exchange 2000 Server
This article was previously published under Q263248

SUMMARY

X.400 message flow in Exchange 2000 Server is different from X.400 message flow in earlier versions of Exchange Server. The changes are based on the architectural changes in Exchange 2000. The Message Transfer Agent (MTA) is still involved with processing X.400 mail, but the routing duties are taken care of by the routing engine.

MORE INFORMATION

Outbound X.400 Messages

Outbound X.400 messages from the information store take the following path:
  1. The message gets passed to Advanced Queuing (AQ) by the store driver (Sd_store.dll to Epoxy to Sd_iis.dll to AQ).
  2. AQ sends the message to the message categorizer.
  3. The categorizer resolves all recipients, expands distribution lists, and so on.
  4. The categorizer sends the message back to AQ.
  5. AQ makes a call "get_next_hop" to the routing engine through Reapi.dll.
  6. The routing engine returns the next hop to the local server. The message is put into the Local Delivery queue in AQ.
  7. The store driver then picks the message up from the Local Delivery queue and submits it to the MTS-In queue in the information store.
  8. The information store submits the message to the MTA and then the MTA makes a call to Mtaroute.dll, which is the MTA's interface to the routing engine. The address of the recipient gets passed to Mtaroute.dll. This address then gets passed to the routing engine which returns the Legacy Distinguished Name (DN) of the connector that the message should be sent outbound on. Again, SMTP makes calls to the routing engine through the file Reapi.dll; the MTA's interface is Mtaroute.dll.
  9. The MTA then delivers message in the same way it delivers messages in Exchange Server 5.0 and 5.5.

Inbound X.400 Messages

Inbound X.400 messages take the following path:
  1. The MTA accepts an inbound message over TCP port 102, processes it and puts it in the local store queue. The store picks up the message from the MTA queue and puts the message in the SMTP MTS-Out store folder.
  2. The transport core store driver picks up the message from this folder and gives it to AQ.
  3. AQ puts the message in the pre-categorizer queue, and eventually sends it to the message categorizer (Phatcat.dll). The message categorizer performs a number of tasks including distribution list expansion, if necessary.
  4. A call is made to the routing engine through Reapi.dll.
  5. Because the store handles the message the same way it handles other messages, the remaining process is the same as the SMTP mail process; the store passes the message off for local delivery, SMTP, or back to the MTA for further routing through other connections.

For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

261103 XCON: A Comparison of the Exchange Server 5.5 Message Transfer Agent and the Exchange 2000 Server Message Transfer Agent

Modification Type:MinorLast Reviewed:4/25/2005
Keywords:kbinfo KB263248
©2004 Microsoft Corporation. All rights reserved.