revised UPN definition

["Paul B. Hill" <pbh@xxxxxxx>]

Definitions section:

User Principal Name (UPN)

An identifier that denotes a unique CU. A UPN is an RFC 822 compliant email 
address and in most cases it is deliverable to the CU. In some cases it is 
identical to the CU's well known email address.  A CU's UPN MUST never be 
deliverable to a different person. It consists of a realm in the form of a 
valid, and unique, DNS domain name and a unique username. In it's simplest 
form it looks like "user@xxxxxxxxxxx".


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Please let everyone know if you disagree or have concerns.

Paul