XFOR: Configuring Transport Selectors with Exchange 5.5 SP1

MORE INFORMATION

The usage of these three fields (A, B, and C) has been changed in the Exchange Server 5.5 Service Pack 1 (SP1) message transfer agent (MTA) to allow multiple links of the same transport type between two MTAs. In particular, the C field is never read by the latest Exchange Server 5.5 SP1 MTA.

When configuring links for an Exchange Server 5.5 SP1 MTA to another Exchange Server 5.5 SP1 MTA, only the B field is required to match on both sides. The settings of the A and C fields make no difference when Exchange Server 5.5 SP1 MTA connects to another Exchange Server 5.5 SP1 MTA.

When configuring links between Exchange Server 5.5 SP1 MTA to an earlier version of Exchange Server (and for our discussion, we will assume the other MTA is in Exchange Server 5.0), then the following rules apply:

• The Exchange Server 5.0 B field must match the Exchange Server 5.5 SP1 B field.
• If the Exchange Server 5.0 C field is configured, then the Exchange Server 5.0 C field must match the Exchange Server 5.5 A field. If the Exchange Server 5.0 C field is not configured, then the Exchange Server 5.0 B field must match the Exchange Server 5.5 A field.

When the Exchange Server 5.5 SP1 MTA connects to a non-Exchange Server MTA with 5.5 SP1:

• A must match the value configured in the foreign MTA for the Exchange Server T-Selector.
• B must match the value configured in the foreign MTA for its own local T-Selector.

For completeness, when configuring an Exchange Server 5.0 MTA to an Exchange Server 5.0 MTA:

• The local A field must match the remote B field (or remote C field, if configured).
• If the local C field is not configured, then the local B field must match the remote A field.
• If the local C field is configured, then the local C field must match the remote A field.