Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site hou3c.UUCP Path: utzoo!watmath!clyde!burl!hou3c!Hornig@SCRC-STONY-BROOK.ARPA From: Hornig@SCRC-STONY-BROOK.ARPA (Charles Hornig) Newsgroups: net.mail.headers Subject: What are SMTP commands "EXPN" and "VRFY" good for? Message-ID: <840917122038.0.HORNIG@PEACE.SCRC.Symbolics> Date: Mon, 17-Sep-84 12:20:00 EDT Article-I.D.: hou3c.839 Posted: Mon Sep 17 12:20:00 1984 Date-Received: Thu, 4-Oct-84 02:07:08 EDT Sender: ka@hou3c.UUCP (Kenneth Almquist) Lines: 45 To: Rich Wales, Header-People@MIT-MC.ARPA In-Reply-To: The message of 15 Sep 84 17:39-EDT from Rich Wales Date: Sat, 15 Sep 84 14:39:52 PDT From: Rich Wales I would like to hear some other people's opinions on the SMTP "EXPN" and "VRFY" commands. I seriously wonder what, if anything, these commands are good for. As everyone probably knows, they are not required in the "minimum" SMTP server implementation, and I can think of very few situ- ations in which a mailer program would ever need (or want) to use them. First, my gripes with EXPN. We (Symbolics) use EXPN solely to support our user-level "Show Mailing List" command. The actual sending of mail does not use it. Now, the problems with VRFY. I have seen only one ARPANET host whose mailer routinely uses VRFY (namely, MIT-MULTICS). Even MIT-MULTICS appears to use VRFY only when relaying mail originating on MAILNET. The scenario seems to be as fol- lows (based on an examination of the various system logs kept by our SMTP server): (1) MIT-MULTICS connects to our SMTP server and issue a VRFY -- which is rejected with a 502 ("command not implemented") reply code. (2) MIT-MULTICS, upon having its VRFY command rebuffed in this manner, does a QUIT and closes the connection. (3) Almost immediately thereafter, MIT-MULTICS connects to our SMTP server again and, without trying another VRFY, sends mail to the user named in the previous session's unsuccessful VRFY. I sent a message to Postmaster@MIT-MULTICS a little while ago asking about this strange behavior, but never received a reply. I also re- cently added code to our SMTP server to implement VRFY (for local user names and mailing lists only), and I'm waiting to see what happens if MIT-MULTICS says VRFY to us and gets a real answer back -- but, so far, there have been no takers. Multics systems send a VRFY when they are acting as a mail relay and receive a RCPT for a non-local recipient. The idea is to make a best effort to get the appropriate error back to the sender syncronously. If the VRFY command is not completed successfully (as was the case above) the mail is accepted anyway for forwarding.