This attribute contains the UPN that is an Internet-style login name for a user based on the Internet standard RFC 822. The UPN is shorter than the distinguished name and easier to remember. By convention, this should map to the user e-mail name. The value set for this attribute is equal to the length of the user's ID and the domain name. For more information about this attribute, see the Naming Properties topic in the Active Directory guide.
In ADAM, this attribute is not required to be in the Internet standard RFC 822 format; it can be a simple name.
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Build date: 7/7/2009
UPN format is described in RFC 822 (obsoleted by RFC 2822)
Snippet from section 6. Address Specification
addr-spec = local-part "@" domain ; global address
local-part = word *("." word) ; uninterpreted ; case-preserved
domain = sub-domain *("." sub-domain)
sub-domain = domain-ref / domain-literal
domain-ref = atom ; symbolic reference
example
admin@mydomain.org