Route Selection Process
The Microsoft Exchange Server MTA compares the recipient address to the addresses in the GWART to determine the group of connectors to which the message can be delivered. The search for a match in the GWART is done in the following order:
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Distinguished name. This address format is searched only if a distinguished name for the recipient has been found. An exact match on the enterprise (organization) and site of the distinguished name is required.
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DDA. An exact, wildcard, or partial match on the domain-defined attribute value (DDAV) is required with an exact or partial match on the domain-defined attribute type (DDAT). Wildcard matches are used in order of the exactness of the match (that is, with the exact match first, followed by the wildcard that has the most matching characters, and so on).
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O/R address. An exact or wildcard match on the address space is required. Each field of the address is compared hierarchically with the contents of the GWART until either a match is found or it is determined that no match is present, at which point this recipient is marked for a non-delivery report (NDR). The order of the search is as follows:
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Country
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Administrative management domain (ADMD)
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Private management domain (PRMD)
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Organization
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Organizational unit
The routing process is used for the following tasks:
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Message and probe routing
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Distribution list expansion (routing to Home-MTA and detecting loops in the distribution list expansion tree)
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Rerouting (all object types)
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Report routing (normal and distribution list-specific)