Email bounce back phenomenon!

Hi Experts

I have found this issue appear on several occasions and I am merely curious as to the cause.

When several users send out emails to some email addresses they receive a non-deliverable bounce back.  When I check the properties of this i discover the email address the email being sent too has changed slightly.  Below is a copy (modified of course) of the properties of the email:


Microsoft Mail Internet Headers Version 2.0
From: postmaster@domain.com
To: sender@domain.com
Date: Tue, 4 Oct 2011 12:29:24 +0100
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
                boundary="9B095B5ADSN=_01CC7D229F6E382400024362emailserver1.do"
X-DSNContext: 335a7efd - 4460 - 00000001 - 80040546
Message-ID: <cxbDaqN6P00000443@emailserver1.domain.com>
Subject: Delivery Status Notification (Failure)

--9B095B5ADSN=_01CC7D229F6E382400024362emailserver1.do
Content-Type: text/plain; charset=unicode-1-1-utf-7

--9B095B5ADSN=_01CC7D229F6E382400024362emailserver1.do
Content-Type: message/delivery-status

--9B095B5ADSN=_01CC7D229F6E382400024362emailserver1.do
Content-Type: message/rfc822

X-MimeOLE: Produced By Microsoft Exchange V6.0.6619.12
Content-class: urn:content-classes:message
MIME-Version: 1.0
Content-Type: application/ms-tnef;
                name="winmail.dat"
Content-Transfer-Encoding: binary
Subject: Follow-up
Date: Tue, 4 Oct 2011 12:29:23 +0100
Message-ID: <EBECAC609C0A574FA55C46E05F40967312BD5732@emailserver1.domain.com>
X-MS-Has-Attach: yes
X-MS-TNEF-Correlator: <EBECAC609C0A574FA55C46E05F40967312BD5732@emailserver1.domain.com>
Thread-Topic: Follow-up
Thread-Index: AcyCiN3lBgy1IrdqQl6h0uvGbQ+8rw==
From: "David McConville" <sender@domain.com>
To: "receiver@receiverdomain.com" <IMCEAMAILTO-receiver+40receiverdomain+2Ecom@domain.com>

Notice the "<IMCEAMAILTO-receiver+40receiverdomain+2Ecom@domain.com>" section where the problem lies. The way I was able to work around this was to instruct the sender to create a contact within outlook containing all the details of the receiver and send the email to the contact rather than the email address and it worked.

Any help on this would be great to either explain whats happening or to prevent the problem from happening again

Thanks
Lee