Microsoft KB Archive/175447

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XFOR: Looping Message from Microsoft Mail to Inet List Server

Article ID: 175447

Article Last Modified on 10/28/2006


  • Microsoft Exchange Server 5.5 Standard Edition
  • Microsoft Exchange Server 4.0 Standard Edition
  • Microsoft Exchange Server 5.0 Standard Edition

This article was previously published under Q175447


This article assumes that the Microsoft Exchange Internet Mail Connector, (IMC), or Internet Mail Service (IMS) and the Microsoft Mail connector are both installed and working correctly. This article also assumes that the IMC or IMS is providing Internet connectivity for Microsoft Mail for PC Networks users via Microsoft Exchange Server's Microsoft Mail connector.

When Microsoft Mail users send mail to a list server on the Internet, there is a possibility that a looping message can be generated.


The following configuration results in the possibility of generating a looping message:

A Microsoft Exchange Server email environment with an IMC or IMS,
and a Microsoft Mail connector installed and running.

The Microsoft Mail connector provides connectivity for Microsoft
Mail users to send mail to the Internet.

In this example, a user on Microsoft Mail sends a subscription request to the list server. The list server sends back an acknowledgement that the user was added to the list. However, if while the message is being routed back to the Microsoft Mail user's mailbox, the Microsoft Exchange PCMTAs (or MSMail MTAs) encounter a problem delivering the mail to a Microsoft Mail 3.x Postoffice (PO), this LISTSERVE acknowledgement message will be sent back to the list server from POSTMASTER (PCMTA or MSMail MTA) with a Non-Delivery Report (NDR).

Causes of a PCMTA or MSMail MTA NDRing a message include:

  • Mailbag contention on the INQUEUE3, outbound PO queue, or the user's KEY and MBG
  • Either the INQUEUE3.KEY, <outbound PO queue>.KEY, or <user-id>.KEY file is full (already containing pointers to 4096 active messages).

This is expected behavior from Microsoft Mail and from the Microsoft Exchange PCMTA service. If the message is not delivered to the recipient, the message is NDR'd.

The problem occurs when the NDR message gets delivered to the list server. The message is now from Microsoft Mail's POSTMASTER to the list server. When the list server receives this email, it is parsed and interpreted as malformed subscription request instead of an NDR. Since the message does not contain the proper syntax for list server "subscription", the list server responds to the email with a new message, typically including instructions and syntax for the proper way to join a list. This response is now destined for the POSTMASTER (PCMTA or Microsoft Mail MTA) account at the PO where the mailbag contention occurred, not to the Microsoft Mail user. So the mail will travel into Microsoft Exchange via the IMC or IMS, get routed to the Microsoft Mail connector (where the address is translated to valid Microsoft Mail <10>/<10>/POSTMASTER syntax) and will route to the POSTMASTER's PO. Unless there has been a POSTMASTER mailbox created on this Microsoft Mail PO (and assuming this mailbox is not full, in other words, less than 4096 messages pending), the message will again NDR because there is no POSTMASTER account on the Microsoft Mail PO.

This loop can be generated every time there is failure to deliver mail from a list server to a Microsoft Mail user. Mailbag contention, and retry timeouts can occur in Microsoft Mail environments, and this can result in the loop.


If a loop is suspected, enabling maximum logging on the MSMI service and performing a "View, Find..." on the application event log specifying the following criteria may aid in tracking down the problem Microsoft Mail file, and the source of the loop on the Internet:

Source: MSExchangeMSMI
Description: POSTMASTER

Considerable recurrence of the following events with the same details may indicate the loop endpoints:

   Source: MSExchangeMSMI
   Category: Routing

      Message ID <xxxxxxxx> processed from INQUEUE

      From: [encapsulated X.400<listserv subscription alias>@<domain>]
      To: <network name>/<po name>/POSTMASTER

   Source: MSExchangeMSMI
   Category: Sent

      Message ID
      <C=xx;A= ;P=xxxx;l=xxxx>
      received from Exchange

      Message ID <xxxxxxxx> created in MS Mail

      From: [encapsulated X.400<listserv subscription alias>@<domain>]
      To: <network name>/<po name>/POSTMASTER

   Source: MSExchangeMSMI
   Category: Debug Data

      Recipient is MS:<network name>/<po name>/POSTMASTER

Once the Internet email domain that is the source of the loop has been identified, the IMC, IMS, or firewall host can be configured to refuse mail from the specific host until the Microsoft Mail file problem is remedied. For the Microsoft Exchange Server, version 5.0 IMS, the IMS Properties, Connections, Accept or Reject by Host, can be configured to reject connections based on IP address. If using an intermediary host between Microsoft Exchange Server and the Internet, consult that host's documentation for information regarding forced connection rejection.

  1. Create a POSTMASTER account on every Microsoft Mail post office so that the message can be delivered. Maintain these mailboxes to ensure they don't fill up.
  2. Create a Microsoft Exchange mailbox to receive the mail. The mailbox should have a Microsoft Mail proxy address created for *each* Microsoft Mail PO. An example is NETWORK/PO1/POSTMASTER. Adding this for each PO as a proxy on the Microsoft Exchange mailbox will enable the list server's mail to be delivered.

NOTE: The MSPROXY.DLL will not generate a POSTMASTER proxy if you create a Microsoft Exchange mailbox called POSTMASTER. Instead, it will generate the Microsoft Mail address of NETWORK/PO/POSTMAST0.

Additional query words: NDR error codepage code page

Keywords: kbprb KB175447