# Note that some SMTP servers accept neither EXPN nor VRFY (the default
# Zmailer configuration, for example).
# - cks
Further, even some that do accept EXPN and VRFY don't always tell you
what you want to know. Actually, they correctly answer they questions
they are asked, but in my experience people often ask the wrong questions.
The example I'm thinking of is a common firewall configuration, where
you have some gateway machine (call it "gateway.company.com") that's
the MX forwarder for "company.com". Mail addressed to
com" isn't actually delivered on that machine, though,
it's handed on in through the firewall to some internal server (call
The common problem I see is that folks wanting to check
com" TELNET to the gateway machine, then do "vrfy user".
The gateway machine quite rightly returns "no such user", since there
_isn't_ any such user ON THE GATEWAY MACHINE. If they had instead
done "vrfy user @
com", they would have gotten back "address OK"
(which still doesn't tell them whether or not the user actually
exists; it just tells them that the gateway knows how to handle mail
addressed to "* @
Brent Chapman Great Circle Associates
COM 1057 West Dana Street
+1 415 962 0841 Mountain View, CA 94041