Michael Orlitzky:
> On 07/12/2010 10:58 AM, Victor Duchovni wrote:
> > On Mon, Jul 12, 2010 at 03:17:49PM +0200, David Touzeau wrote:
> >
> >> smtp-amavis unix - - n - 7 smtp
> >> -o smtp_data_done_timeout=1200
> >> -o smtp_send_xforward_command=yes
> >> -o disable_dns_lookups=yes
> >
> > I notice people still using "disable_dns_lookups=yes" long after the
> > reason for doing so became moot.
> >
> > This setting is no longer necessary for content filters, and is rarely,
> > if ever, necessary otherwise. It should be removed from HOWTO guides, ...
> >
>
> If you don't mind, why was it necessary, and why isn't it any longer?
> I've still got it on my amavisd-new instance, and have long forgotten
> where it came from.
The combination of
1) Postfix sending up to 50 recipients per mail transaction.
2) Sending mail for recipients in multiple domains through a
single content filter or gateway host.
3) DNS CNAME expansion of domains in MAIL FROM/RCPT TO commands.
(Postfix no longer does this expansion.)
4) ESMTP command pipelining, meaning that the SMTP client could
buffer up a lot of commands before sending them to the server.
(The Postfix SMTP client now flushes output if the buffered data
is getting old.)
These together could result in the SMTP server timing out when
the DNS CNAME lookups were slow.
Wietse
