Hello, We have a very small Exchange 2003 organisation with only one (1) Exchange 2003 Server that we want to upgrade to Exchange 2007. Our finalised Exchange 2007 organisation will only be a single server also. We have a third-party mail filter product that is installed on the same server as our Exchange 2003 server. As such the third-party mail filter utilises the default port 25. Exchange 2003 uses another portfrom its SMTP activities (to receive email to and send mail from), and has until now been relaying all Internet mail to the third-party mail filter product as its smarthost. The Exchange 2007 server has been installed into the organisation. In Exchange 2007, the SMTP protocol is provided by the Microsoft Exchange Transport service ( MSExchangeTransport.exe ). I presume therefore that communication from the Exchange 2007 server to the Exchange 2003 server is therefore done by Microsoft Exchange Transport service. Problem for me is that Microsoft Exchange Transport service talks to a destination port of 25 by default. Remember that on our Exchange 2003 server this means it tries to have a conversation with a third-party mail filter product. For the Exchange2007 server to have a conversation direct to our Exchange2003 server the Exchange2007 Microsoft Exchange Transport service needs to talk to another port. Is there any easy way to do this ? Like - Can the Exchange2007 Microsoft Exchange Transport service somehow be directly or indirectly configured to talk to an alternative destination port other than port 25 ? Other suggestions about how to get around this issue would also be welcomed. However we do not really have hardware just sitting aboutwaiting so if I can avoid moving applications to different or separate machines then that would be preferred.