It appears these messages differ from Zimbra Connector-sent meeting requests significantly.
I've "sanitized" it a bit - to protect the innocent. <grin>
Code:
Received: from localhost (localhost.localdomain [127.0.0.1])
by mailhost.example.com (Postfix) with ESMTP id 405CFCAECABE
for <emailaddress2@example.com>; Tue, 17 Jul 2007 14:25:40 -0700 (MST)
X-Virus-Scanned: amavisd-new at
X-Spam-Score: -2.526
X-Spam-Level:
X-Spam-Status: No, score=-2.526 tagged_above=-10 required=6.6
tests=[AWL=0.073, BAYES_00=-2.599]
Received: from mailhost.example.com ([127.0.0.1])
by localhost (mailhost.example.com [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id 9j95rXhwZn7e for <emailaddress2@example.com>;
Tue, 17 Jul 2007 14:25:37 -0700 (MST)
Received: from mailhandler.example.com (mailhandler.az.example.com [209.63.44.136])
by mailhost.example.com (Postfix) with ESMTP id 7C31DCAECABD
for <emailaddress2@example.com>; Tue, 17 Jul 2007 14:25:37 -0700 (MST)
X-ASG-Debug-ID: 1184707536-056f00280000-U5Kqtq
X-Barracuda-URL: http://mailhandler.example.com:8000/cgi-bin/mark.cgi
X-Barracuda-Connect: mail.mn.example2.com[216.243.150.98]
X-Barracuda-Start-Time: 1184707536
X-Barracuda-Encrypted: DHE-RSA-AES256-SHA
X-ASG-Whitelist: Sender
Received: from mail.mn.example2.com (mail.mn.example2.com [216.243.150.98])
(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))
(No client certificate requested)
by mailhandler.example.com (Spam Firewall) with ESMTP id 24A8F27903
for <emailaddress2@example.com>; Tue, 17 Jul 2007 14:25:37 -0700 (MST)
Received: from TINA (pool-71-252-162-91.dllstx.fios.verizon.net [71.252.162.91])
by mail.mn.example2.com (Postfix) with ESMTP id B456DEB96B
for <emailaddress2@example.com>; Tue, 17 Jul 2007 16:25:27 -0500 (CDT)
From: "Sending User" <sendingemail@example2.com>
To: <emailaddress2@example.com>
X-ASG-Orig-Subj: Test meeting request
Subject: Test meeting request
Date: Tue, 17 Jul 2007 16:25:39 -0500
Message-ID: <029601c7c8b9$06084a20$6f00a8c0@TINA>
MIME-Version: 1.0
Content-Type: text/calendar; method=REQUEST;
charset="utf-8"
Content-Transfer-Encoding: 7bit
X-Mailer: Microsoft Office Outlook 11
Thread-Index: AcfIuQW0bfFVlRJJTtGd/diV5uk5SQ==
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138
X-Barracuda-Virus-Scanned: by Barracuda Spam Firewall at example.com
BEGIN:VCALENDAR
PRODID:-//Microsoft Corporation//Outlook 11.0 MIMEDIR//EN
VERSION:2.0
METHOD:REQUEST
BEGIN:VEVENT
ATTENDEE;ROLE=REQ-PARTICIPANT;RSVP=TRUE:MAILTO:emailaddress2@example.com
ORGANIZER:MAILTO:sendingemail@example2.com
DTSTART:20070721T130000Z
DTEND:20070721T133000Z
TRANSP:OPAQUE
SEQUENCE:0
UID:040000008200E00074C5B7101A82E00800000000F059DC1C8FC8C7010000000000000000100
0000078C1B9939F83AA4FB90D8ABB696F6E0C
DTSTAMP:20070717T212539Z
DESCRIPTION:When: Saturday\, July 21\, 2007 8:00 AM-8:30 AM (GMT-06:00)
Central Time (US & Canada).\n\n*~*~*~*~*~*~*~*~*~*\n\nHere you go. I
should note that I'm not on Zimbra yet and am just using outlook to send
my invitations.\n
SUMMARY:Test meeting request
PRIORITY:5
X-MICROSOFT-CDO-IMPORTANCE:1
CLASS:PUBLIC
BEGIN:VALARM
TRIGGER:-PT15M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR
I've got an interesting screenshot attached as well.
Bugzilla
Wiki
Source
Empty meeting requests 
I've deleted the duplicates.
Linear Mode
