XCON: What Message Categorization in Exchange 2000 Server Involves (233363)

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Upon receiving the message (by means of a IMSG interface) from the Advanced Queuing engine, the Message Categorizer in Exchange 2000 Server performs several steps:

1. It resolves the envelope Sender and searches for that address in proxyAddresses attributes in the directory service in order to resolve it.
2. It resolves the envelope Recipient list and searches for each address in proxyAddresses attributes in the directory service in order to resolve it.
3. If the envelope Recipient list includes distribution groups (the Windows 2000 equivalent of Distribution Lists), it expands the Recipient list to include those members if expansion is allowed on this server.
4. If any recipient cannot be resolved, it marks that recipient as unknown.
5. It applies any per-sender and per-recipient limits, and marks recipients appropriately.
6. It bifurcates the message in case multiple copies of the message need to be created because different recipients have different properties set.
   
   NOTE: An example of this case is when the message with read receipt request is sent to a hidden DL and an additional individual in the To line. Because the membership of hidden DL is expected to be confidential, you do not want the read receipts to be generated. In this case, two copies of the message are created, one for the hidden DL and the other for the single recipient as the read receipt request will have to be stripped from the message destined for the hidden DL.
7. It marks each recipient as either "Gateway" (meaning that the recipient is reachable through the message transfer agent [MTA]) or "Local" (meaning that the recipient is actually on a Exchange 2000 store).

After categorization, the message gets put into a per-destination-domain queue inside Advanced Queuing.