Delayed and NDR emails

I manage a 2003 Exchange Server SP2. A remote user is attempting to send emails to users on the server I manage. The remote user can send to 2 of 5 users. The other 3 generate delayed messages and then NDR's. I have added the remote users domain to our allowed spam filter. I have checked that my server is not listed on any RBL's, the DNS, MX, PTR records are all correct. Here are the 2 messages/headers the sending user receives, first is the delay, second will be NDR. I am not sure what else to check at this point since the emails will get through to 2 of the 5 users. i have changed domain names

**********************************************************************************************************************

From: Mail Delivery Subsystem <mailer-daemon@googlemail.com>
Date: Wed, Mar 30, 2011 at 11:07 AM
Subject: Delivery Status Notification (Delay)
To: ctroy@blankdomain.com


This is an automatically generated Delivery Status Notification

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

Delivery to the following recipient has been delayed:

    mcrosland@blankdomain2.com

Message will be retried for 1 more day(s)

Technical details of temporary failure:
Connection was dropped by remote host (SENT_MAIL)

----- Original message -----

MIME-Version: 1.0
Received: by 10.223.55.201 with SMTP id v9mr4499577fag.76.1301321835250; Mon,
 28 Mar 2011 07:17:15 -0700 (PDT)
Received: by 10.223.26.137 with HTTP; Mon, 28 Mar 2011 07:17:14 -0700 (PDT)
Date: Mon, 28 Mar 2011 10:17:14 -0400
Message-ID: <AANLkTi=jMEU6D-p0NoCZnFZpJ8ineO4aeO7+NfqXd8-E@mail.gmail.com>
Subject: bio
From: Colleen Troy <ctroy@blankdomain.com>
To: "Malcolm M. Crosland" <mcrosland@blankdomain2.com>
Content-Type: multipart/mixed; boundary=001517478f92ba9ea5049f8b9979

**********************************************************************************************************************

From: Mail Delivery Subsystem <mailer-daemon@googlemail.com>
Date: Mon, Mar 28, 2011 at 10:24 AM
Subject: Delivery Status Notification (Failure)
To: ctroy@blankdomain.com


Delivery to the following recipient failed permanently:

    mcrosland@blankdomain2.com

Technical details of permanent failure:
Connection was dropped by remote host (SENT_MAIL)

----- Original message -----

MIME-Version: 1.0
Received: by 10.223.15.92 with SMTP id j28mr1100652faa.56.1301071006578; Fri,
 25 Mar 2011 09:36:46 -0700 (PDT)
Received: by 10.223.26.137 with HTTP; Fri, 25 Mar 2011 09:36:45 -0700 (PDT)
Date: Fri, 25 Mar 2011 12:36:45 -0400
Message-ID: <AANLkTik1vuFpdK3J6A8=K5R0fM1+BTBPpvRhmhS9g66j@mail.gmail.com>
Subject: release and photo
From: Colleen Troy <ctroy@blankdomain.com>
To: "David T. Pearlman" <dpearlman@blankdomain2.com>
Cc: "Malcolm M. Crosland" <mcrosland@blankdomain2.com>
Content-Type: multipart/mixed; boundary=0015174483182cd6d0049f5133ab

**********************************************************************************************************************

The user is utilizing a gmail account but the domain is not gmail.
CNEAdminAsked:
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FDiskWizardCommented:
That could be a lot of things. did they send the exact same email to the 5 people? ruling out Attachments types, etc..? What is in the email? There is an issue with Meeting requests between Exchange 2003 and 2007 systems.

Security of some sort on your side could drop the connection if it sees something wrong.
And a 'delay' is exactly what you would see if a message is just being dropped.

IPS? Anti-virus? Blacklists? It could be that emails from them come from 2 different IPs and one is blacklisted... I've seen that before. Some small shops sometimes use a shared SMTP server for outbound @ their provider. All it takes is one client of that ISP to send a load of SPAM and they may get blacklisted at least short term.
You said you checked if you were blacklisted.. what about them?

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mikerigelTech Support AnalystCommented:
Check your Spam Filter logs.  Do you see where it is being blocked?  Turn off your SPAM filter and have them send as a test.  Does it get through?  Sounds like your spam filter does a SMTP check.
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CNEAdminAuthor Commented:
The issue is intermittent so it looks like a possible greylisting issue of the sending domain and the google email server.. I am not sure if I can do anything to work around or even resolve this.
0
CNEAdminAuthor Commented:
The issue has misteriously gone away so I am closing the question and not awarding any points.
0

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CNEAdminAuthor Commented:
The issue went away without any intervention on my part
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