Unspecified Error (SENT_MESSAGE): Connection timed out

Good Morning folks,

I am having some difficulty with an exchange 2007 server, platform is SBS 2008.  Gmail users can not send email to users on this exchange box when attachments are included.

if they just send a plain text email it comes in right away!

after a few days they get a kickback saying "Unspecified Error (SENT_MESSAGE): Connection timed out" and when I pull the exchange logs there was never an attempt to pass the message into the server.  Gmail did not even connect.

the exact message is (edited to remove user emails):
===============================
From: Mail Delivery Subsystem <mailer-daemon@googlemail.com>
Date: Sat, Mar 24, 2012 at 12:23 PM
Subject: Delivery Status Notification (Failure)
To: xxxxx@xxxxxx.com


Delivery to the following recipient failed permanently:

    xxxxx@xxxxxxcontracting.com

Technical details of permanent failure:
Unspecified Error (SENT_MESSAGE): Connection timed out
=================================


I'm at a total loss on this and mxtoolbox says everything is happy.  green checkmarks all across the board, i can't find us on any RBL's and am wondering if anyone else has seen this before?

Many thanks!
Justin
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mrjking2000Asked:
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Rajkumar-MCITPCommented:
did you check the allowed email received limit to your organization? emails from gmail are less than the limit?

for testing send a email from gmail to internal user more than the allowed limit and search the email queue using queue viewer and if it not there, perform a message tracking

On the NDR email received in Gmail, check the email header to know whether the email reached your organization? or the NDR generated from ur exchange or not etc..
mrjking2000Author Commented:
incoming and outgoing email limits are 30 MB, the email in question was 2.5 MB in size.  The NDR was not generated from the exchange box.

message tracking doesn't even show the email getting to the exchange server at all.
suriyaehnopCommented:
Do you have anti-spam(Mail Gateway) installed between CAS server?

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mrjking2000Author Commented:
there is no anti-spam device before the server, i do have a sonicwall TZ170 doing a very basic gateway level virus scan.  I disabled that on inbound SMTP.  we will see what happens.
mrjking2000Author Commented:
UPDATE: i disabled the SMTP service monitoring and my initial test from a gmail account came right in with an attachment, i'm going to let this ride for a few days and see if the problem is resolved.

thanks,
mrjking2000Author Commented:
well for now this does seem to be resolved.  i would have never thought that sonicwall was chewing up the traffic.

many thanks!!
mrjking2000Author Commented:
thank you both!  I did check the receive connector settings and also make adjustments there, but the total end was the sonicwall which was monitoring SMTP traffic.
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