Prior to RFC1123, a successful reply to the
SMTP VRFY command was always prefixed with a 250, meaning that
sending to this address was likely to result in successful delivery:
250 firstname.lastname@example.org (Full Name)
Here, sendmail states (with the
250) that it interpreted the address as
valid locally and that delivery or relaying to
another site would be attempted.
RFC1123 now requires that shades of meaning be conveyed in that
success code, so the correct prefix should be 252, which means that
the host will accept the address and might
attempt to relay it elsewhere.
If the F=q delivery agent flag is set,
sendmail returns the 250 prefix; otherwise, it
returns the 252 prefix. It should be set only for delivery agents
doing local delivery. For configuration files earlier than version 7,
the F=q delivery agent flag is automatically set
for the local, prog, and
*file* delivery agents.