Oops , it is actually RFC1123 that requires the VRFY command. Since disabling
the VRFY command is permitted, it also seems like we should define another
reply code which simply indicates such. For example: 25n Cannot VRFY user.
This command is disabled.
Excerpt from RFC1123:
5.2.3 VRFY and EXPN Commands: RFC-821 Section 3.3
A receiver-SMTP MUST implement VRFY and SHOULD implement EXPN
(this requirement overrides RFC-821). However, there MAY be
configuration information to disable VRFY and EXPN in a
particular installation; this might even allow EXPN to be
disabled for selected lists.
A new reply code is defined for the VRFY command:
252 Cannot VRFY user (e.g., info is not local), but will
take message for this user and attempt delivery.
Mike