Illegal command pipelining by lists.gnu.org (209.51.188.17)

[Michael Orlitzky]

Hi, I ran into a problem while trying to subscribe to bug-gnu-emacs. My 
subscription confirmations weren't coming through. I checked the mail 
logs, and the root cause seems to be that lists.gnu.org (209.51.188.17)
is being rejected by postfix's "postscreen_pipelining_enable = yes" 
check, which looks for incorrect SMTP implementations. We have this 
enabled on our MX to deter some spam bots.

The relevant feature is described at,

  http://www.postfix.org/POSTSCREEN_README.html#pipelining

And my logs for one of the sessions:

  Nov  9 08:18:19 mx1 postfix/postscreen[10830]: NOQUEUE: reject: RCPT
  from [209.51.188.17]:40601: 450 4.3.2 Service currently unavailable;
  from=<bug-gnu-emacs-bounces+michael=address@hidden>,
  to=<address@hidden>, proto=ESMTP, helo=<lists.gnu.org>

  Nov  9 08:18:19 mx1 postfix/postscreen[10830]: COMMAND PIPELINING from
  [209.51.188.17]:40601 after BDAT: Received: from localhost([::1]:36782
  helo=lists1p.gnu.org)\r\n\tby lists.gnu.org with esmtp (Exim 4.90

This was fixed in Exim, it looks like,

  https://bugs.exim.org/show_bug.cgi?id=2454

but I wanted to prod you about upgrading because we can't turn that 
feature off and you're probably dropping a significant chunk of mail due 
to it.