PMDF System Manager's Guide
PMDF-REF-6.0

Centralized naming is used when you wish to have all incoming messages use a uniform, centralized addressing format (e.g., John.Doe@acme.com) which you will convert to internal addresses, and for outbound mail have all instances of internal addresses converted to the uniform, centralized format.^b The advantages to centralized naming include enhanced security as the outside world does not see actual host names or user names, stability in that mail addresses do not become outdated as internal host names change or employees and students change accounts, and ease of use for users in the outside world when the centralized naming scheme replaces possibly awkward internal mailbox names with more presentable and mnemonic mailbox names.

Note

^b Note that although a single, "central" host name is used by the outside world, this does not mean that all mail from the outside world must flow through a single, central host. For instance, on the Internet, DNS MX records may be used to equate several hosts with the central host name. Preferences may be associated with each host so equated.