ENUM
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... message routing based on one of two mechanisms. The
most complete service should use the ENUM address resolution service
...
... The more basic send-and-pray message service uses only the ENUM
service and MX records to route the message to the intended
recipient's domain ...
... email address.
The client SHOULD use the ENUM service to retrieve the identity of
the VPIM Directory ...
...
The VPIM directory server is found by using the ENUM protocol and
querying for the VPIMDIR service ...
...
The exposure of email addresses through the ENUM service
provides a bulk mailer access to large numbers of email
addresses where only the telephone number ...
... URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761prop, April 2004. ...