XCON: How Exchange Server Routes One-Off Messages Internally (262112)

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A one-off address is an e-mail address that does not directly resolve as a valid address in the global address list. Although the address is not resolved by the global address list or personal address book, it is underlined as if it were resolved.

NOTE: Although most e-mail protocols, such as cc:Mail or MS Mail, require you to use brackets ([]) with one-off addresses to denote the type of address and the routing, Simple Mail Transport Protocol (SMTP) does not require information about the type of address in the mail address.

When a one-off address is routed through Exchange Server, the directory associates the address as a domain defined attribute (DDA) in the local X.400 Site-Proxy-Space. DDA is an X.400 attribute that allows other systems to map their address directly to an X.400 O/R address. For example, an e-mail message sent to user@microsoft.com is defined as "C=us;a= ;p=Org;o=Site;dda=SMTP:user@microsoft.com", and then routed by DDA.

If a DDA route is not available, the message transfer agent (MTA) route uses the X.400 address. In some instances, an X.400 connector with an address space of "C=*" may cause messages with an SMTP one-off address to attempt routing through an X.400 connector, and not an SMTP connector. Typically, the message loops when re-routed back to the originating site.

Exchange Server routes all one-off addresses by the process described above. Custom recipient messages, although similar to one-off messages, are routed through a different process.

For additional information about custom recipient message routing, click the article number below to view the article in the Microsoft Knowledge Base: