David F. Skoll wrote:
On Wed, 3 Nov 2004, Aleksandar Milivojevic wrote:
This is because we have only "error" built-in mailer in Sendmail. If we
had "disconnect" built-in mailer, things would probably be a bit different.
From reading the Sendmail source code, it looks like Sendmail 8.13.1
treats a 421 reply code from a milter "magically", and shuts down the
connection. See line 3376 of sendmail/milter.c and line 848 of
sendmail/srvsmtp.c. I do not believe this "feature" exists in Sendmail
8.12.x.
It looks like some rule sets can also force the connection to be terminated
by returning 421.
Not treating it magically. It treats it logically. ;-)
421 is used when server side of connection must close its end. For
example, if you send SIGTERM to Sendmail (or any other MTA), it *must*
attempt to asynchroniously send 421 to all connected clients before it
exits, in the hope that client will pick it up when it tries to issue
next command. Basically, it is a way to say client "Something is
killing me, I wan't be able to finish this transaction, try again
later". Basically, after sending 421, there's no point in keeping the
connection open anymore.
I've attempted to put this into access file on 8.12.x, and also to send
it from MIMEDefang, and Sendmail doesn't close the connection. So I
guess it is something new in 8.13.x.
Also 4xx codes are temp failures, instructing client to try again
later... So there are some drawbacks in case of false positives. For
starters. Legitimate senders will not be notified right away that teir
mail hasn't made it (usually delay of around 5 days). If filter becomes
trigger happy, bunch of sites will constantly retry to deliver bunch of
emails to you (which is good and bad, you can quicly fix the filter
before anything is permanently rejected)... I guess this works nicely
with logic behind Can-It?
--
Aleksandar Milivojevic <[EMAIL PROTECTED]>Pollard Banknote Limited
Systems Administrator 1499 Buffalo Place
Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
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