Loop in the received mails

Hello,

When I received a message from the external, I have a "loop" in my mail flow. I have not a problem with the receiving but it is strange.

My headers are the follow :

Received: from exchsrv.domain.com (192.168.1.x) by exchsrv.domain.com
 (192.168.1.x) with Microsoft SMTP Server (TLS) id 15.0.1044.25 via Mailbox
 Transport; Fri, 24 Apr 2015 13:05:07 +0200
Received: from exchsrv.domain.com (192.168.1.x) by EXCHSRV.domain.com
 (192.168.1.x) with Microsoft SMTP Server (TLS) id 15.0.1044.25; Fri, 24 Apr
 2015 13:05:07 +0200
Received: from antispam (192.168.1.x) by exchsrv.domain.com (192.168.1.x) with
 Microsoft SMTP Server id 15.0.1044.25 via Frontend Transport; Fri, 24 Apr
 2015 13:05:07 +0200

Note the uppercase in the second receive.

I do not really understand when the problem could be.

Thanks