At 10:05 +0300 on 06/16/2007, Kari Hurtta wrote about draft-klensin-rfc2821bis-04: VRFY and EXPN syntax:
--- start quote ------ "User name" is a fuzzy term and has been used deliberately. An implementation of the VRFY or EXPN commands MUST include at least recognition of local mailboxes as "user names". However, since current Internet practice often results in a single host handling mail for multiple domains, hosts, especially hosts that provide this functionality, SHOULD accept the "[EMAIL PROTECTED]" form as a "user name"; hosts MAY also choose to recognize other strings as "user names". --- end quote ------ However later actual syntax seems not allow "@domain" which is "SHOULD" on here.
When a SMTP Server hosts multiple domains (at least when Virtual Hosting), it knows (or should know via the FQDN passed when the remote client connects) which domain it is acting as. Thus a Local-Part only should be adequate. A note in the quote above of the requirement that it knows who it is acting as might be helpful to clarify the situation.
