Question : Exchange Queues filling with error 'The connection was dropped due to an SMTP protocol event sink'

The system is a MS Small Business Server. Recently installed Service Pack 2 for Windows Server 2003. In the last few days, a number of message queues (outgoing/SMTP) are failing to connect with the error described above. Event log reports:
Event Type:      Warning
Event Source:      MSExchangeTransport
Event Category:      Connection Manager
Event ID:      4007
Date:            16/11/2007
Time:            10:51:35
User:            N/A
Computer:      SERVER
Description:
Message delivery to the host '193.111.201.135' failed while delivering to the remote domain  'iper.co.uk' for the following reason: The connection was dropped due to an SMTP protocol event sink.
 The SMTP verb which caused the error is 'quit'.  The response from the remote server is ''.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
Data:
0000: f3 02 04 c0               ó..À    
I've run smtpdiag tool on the machine and all test pass in the verbose mode.
In front of the server is a Prodigy PRO firewall from GSEC1 which is running a transparent SMTP proxy.
Anyone have any pointers?

Answer : Exchange Queues filling with error 'The connection was dropped due to an SMTP protocol event sink'

Hi

You may want to forward emails to your ISP Mail Relay Host. Give them a call and ask them the host/IP for this. This will take load off of your system and can sort out issues like this.
You will need to re-run the CEICW Wizard to input the host address. I use this method everywhere I can to simply take load off of the Internet connection at that office and get rid of error messages like these.