First a description of our email flow:
We have Outlook (2003 on desktop or 2007 on TS)
email server is Exchange 2003 w/Trend Micro ScanMail
From Exchange it goes to an ISA server 2006 w/Trend Micro IMSS
It then goes to a Barracuda that is set for incoming so it doesn't do any checking on outgoing.
Now the issue
We have an attorney that we email with several times a day. Most email goes through both ways without a problem. However every once in awhile an email being sent TO the attorney goes into the Exchange Internet Queue and sits there retrying until it times out and returns an NDR.
I can track all messages through the entire system except the ones that sit in the Exchange queue. They never seem to leave the Exchange server.
The NDR is:
Could not deliver the message in the time limit specified. Please retry or contact your administrator.
The message in the application event log is:
Event Type: Warning
Event Source: MSExchangeTransport
Event Category: Connection Manager
Event ID: 4006
Time: 7:43:57 AM
Computer: <our exchange server>
Message delivery to the host 'x.x.x.x' failed while delivering to the remote domain '[x.x.x.x]' for the following reason: The connection was dropped by the remote host.
For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp
0000: d3 02 04 c0 Ó..À
The IP address is the ISA server. All other email is going through. There appears to be no consistancy to the emails that are blocked. Some have attachments and some don't. None of them are very big. The one today was on 166K.