Why are we receiving large numbers of "not read" receipts at 1:05 am each day

What is the title of the message? There is a sender? It seems that someone might be firing emails through a robot, if you can identify the sender, I suggest a clean

The senders are all internal employees.  The receipts appear to be legitimate at the subject lines relate to company matters.  I have been unsuccessful however in determining when the original meeting requests were sent.  I tried to search on the subject line but could not find them.  The receipt does not indicate when they were originally sent.

I do not know of any maintenance of the Exchange asking for confirmation of reading to any customer. Another thing that can help is to know the recipient, which e-mail he received ... try the reverse path of unread messages.

Have you tried right-click the message and go into options? there you'll see information about the message, information such as: server output, plots of origin, destination machine etc ...

try this ...

Paste what you find in message options here

Since the receipts all reflect senders and recipients within our company I did try to search from both directions with no luck.  The following is the information from one of the receipts:

Received: from RIGGEXCHG.rdgins.com ([fe80::e83f:75dc:949e:c550]) by
 RiggExchg.rdgins.com ([fe80::e83f:75dc:949e:c550%11]) with mapi; Sun, 19 Sep
 2010 01:05:21 -0400
From: "Lindsay C. Skinner, CISR, CPIA" <lskinner@rdgins.com>
To: "Robert E. Rigg, CPCU, CIC, CLU" <rrigg@rdgins.com>
Subject: Not read: Accepted: Selective Insurance
Thread-Topic: Selective Insurance
Thread-Index: Acr3WVEj29LQZ3zSQ3GIFUcA6o9q9QAAAAMgAGb3uboXsMR30w==
Date: Sun, 19 Sep 2010 01:05:20 -0400
Message-ID: <044AD02FB0490949BD4FA0852AA4EEF10DFB8520@RiggExchg.rdgins.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-Exchange-Organization-SCL: -1
X-MS-TNEF-Correlator:
Content-Type: multipart/report;
      boundary="_000_044AD02FB0490949BD4FA0852AA4EEF10DFB8520RiggExchgrdgins_";
      report-type=disposition-notification
MIME-Version: 1.0
X-MS-Exchange-Organization-AuthSource: RiggExchg.rdgins.com
X-MS-Exchange-Organization-AuthAs: Internal
X-MS-Exchange-Organization-AuthMechanism: 04

Strange, it seems that this RIGGEXCHG.rdgins.com sending messages late. as if the messages were in a queue. I found an article about delay in sending messages:
http://support.microsoft.com/kb/196072/pt-br

All the recipients are receiving the confirmation messages right? nobody gets the original message?

With 90% certainty, that the Exchange with some configuration accordingly activated. I am no expert on it, but worth a look at issues related to it.

No one really offered a solution to this but I wish to close the question