This has happened to me several times recently; has never happened until a couple of weeks ago.
From the https://mail.google.com/mail/ web-interface, Cc an alias
on my server, which expands to, amongst other things, my gmail.com email address; a bounce is immediately received in the thread (apparently, gmail doesn't reject the bounces from the very same server from which some messages are rejected). Most likely cause: too many domain names from the mtr(8) output in the message.
Same for sending a similar message directly from my own server, directly to my gmail.com address, being in the Cc field: a bounce is received within my own server, no message is received at gmail. The bounce from such an experience is at the end of this message.
I consider this a major outage: how many other valid semi-automated emails addressed to myself have been unfairly rejected by gmail on the SMTP level recently?
I also now know why my gmail.com address has been unsubscribed from several mailing lists over this summer, citing excessive bouncing. My own mailserver wasn't even involved:
<<##
Delivered-To: mureninc@gmail.com
Received: by 10.114.5.70 with SMTP id q6csp13073ldq;
Tue, 10 Sep 2013 03:43:00 -0700 (PDT)
X-Received: by 10.204.76.203 with SMTP id d11mr18914232bkk.3.1378809779724;
Tue, 10 Sep 2013 03:42:59 -0700 (PDT)
Return-Path: <lm-sensors-bounces@lm-sensors.org>
Received: from flocki.atrpms.net (m.at.physik.fu-berlin.de. [160.45.254.30])
by mx.google.com with ESMTPS id zk7si1773373bkb.190.1969.12.31.16.00.00
(version=TLSv1 cipher=RC4-SHA bits=128/128);
Tue, 10 Sep 2013 03:42:59 -0700 (PDT)
Received-SPF: neutral (google.com: 160.45.254.30 is neither permitted nor denied by best guess record for domain of lm-sensors-bounces@lm-sensors.org) client-ip=160.45.254.30;
Authentication-Results: mx.google.com;
spf=neutral (google.com: 160.45.254.30 is neither permitted nor denied by best guess record for domain of lm-sensors-bounces@lm-sensors.org) smtp.mail=lm-sensors-bounces@lm-sensors.org
Received: from localhost ([::1] helo=m.at.physik.fu-berlin.de)
by flocki.atrpms.net with esmtp (Exim 4.80.1)
id 1VJLPJ-0001fB-QJ
for mureninc@gmail.com; Tue, 10 Sep 2013 12:42:59 +0200
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit