XFOR: Message Loop Created between Exchange and Microsoft Mail for AppleTalk Networks (164850)

SYMPTOMS

You may experience a problem in which a message loops back and forth between Microsoft Mail for PC Networks and Microsoft Exchange Server. Three things must hold true for this to occur:

A Macintosh Distribution List (DL) is created that contains an Exchange Server DL (which was imported by means of the Exchange Server Connection Directory Exchange Requestor [DER] or by means of a manual Import).
The Exchange Server DL contains a Macintosh User (or an Exchange Server user who has been configured to have an Alternate Recipient that is a Macintosh user).
A Macintosh user submits a message to the Macintosh DL.

RESOLUTION

To prevent the loop, you must create a Custom Recipient on the Exchange Server computer for the Macintosh DL. To do this, follow these steps:

If the Macintosh DL is called MAC DL@MACSERVER, create a Custom Recipient of the e-mail address type: MacMail Address.
In the MacMail Address properties page, enter the Distribution List Name in the User Name field and the Macintosh server name in the Server Name field.
Display Name:MAC DL@MACSERVER (Or whatever you like)
User Name:MAC DL
Server Name:MACSERVER
To completely remove all cases of message loops, the DER should be used to fully import all Microsoft Mail addresses into Exchange Server (or else do a manual import of all addresses).

MORE INFORMATION

In this situation, the message is delivered to all recipients listed in the Macintosh DL. Because it contains a foreign mail address (the Exchange Server DL), the message is submitted to the Exchange Server Connection gateway, which in turn moves the message over to the Exchange Connector postoffice (in the Mactopc directory).

On Exchange Server, the message is picked up by the Microsoft Mail Connector (AppleTalk) message transfer agent (MTA) and it moves it from the Mactopc directory to the Exchange Connector postoffice.

The MS Mail Connector Interchange (MSMI) takes the message and sends it to the Exchange Server computer. The server expands the DL and delivers the message to each recipient. When the Macintosh user is encountered in the DL, the message is sent back to the MS Mail Connector (AppleTalk) in the reverse path.

The MS Mail Connector (AppleTalk) takes the message, and moves it to the location in the Exchange Connector postoffice (the Pctomac directory) where the Microsoft Exchange Connection gateway is expecting new messages. During this activity, the MS Mail Connector (AppleTalk) assumes responsibility for submitting any address found in the message that is an AppleTalk address type (MS Mail [AppleTalk]), including the original Macintosh DL that the Macintosh user originally submitted the message for.

When the message is finally received again by the Microsoft Mail for AppleTalk Networks server, it resubmits the message to the Macintosh DL, which causes the loop.

Correcting the Message Loop

When an AppleTalk address (MS Mail [AppleTalk]) is received by Exchange Server from the MSMI, the address is compared to all the custom recipient (CR) addresses.

If a match is found, the directory name for the matching CR is used for routing purposes while in Exchange Server. On its way back out of the MSMI, it will be sent to the custom recipient's Microsoft-type address (changed to CSI address types when handled by the MS Mail Connector [AppleTalk]).

For instance, a Macintosh user who has an address of (as viewed by the MS Mail Connector [AppleTalk])

   TYPE: MSMAIL (MSA)
   USER: MACUSER@MACSERVER

and a CR in Exchange Server, the address would be converted on its way back out the MSMI to

   TYPE: CSI
   USER: NET/PO/MACUSER

When the MS Mail Connector (AppleTalk) looks at a message to be handled, it will not assume responsibility for this address because it only assumes responsibility for MS Mail-type addresses.