XFOR: Looping Message from Microsoft Mail to Inet List Server

• Microsoft Exchange Server, version 4.0
• Microsoft Exchange Server, version 5.0

SUMMARY

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.

MORE INFORMATION

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.

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).

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.

Detection:

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

   2444
   Source: MSExchangeMSMI
   Category: Routing
   Description:

      Message ID <xxxxxxxx> processed from INQUEUE

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

   2448
   Source: MSExchangeMSMI
   Category: Sent
   Description:

      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

   10000
   Source: MSExchangeMSMI
   Category: Debug Data
   Description

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

WORKAROUND

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.

   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.