Question : Lock Down TCP 25 on MS Exchange 2003

We have subscribed to a 3rd party Spam Filter and we need to lock down our mail port per these instructions:
2. Lock Down Your Mail Port
In order to prevent senders from bypassing filtering by connecting directly to your network, it is
recommended that your mail port be locked down to deny unauthorized access. For your reference,
the IP subnets currently hosting filtering service mail servers are listed below.
       Filtering Service IP Subnets:
       208.65.144.0/21               (208.65.144.0 - 208.65.151.255)
       208.81.64.0/22                (208.81.64.0 - 208.81.67.255)
       Used by Support to Troubleshoot:
       63.149.241.32/27              (63.149.241.32  63.149.241.63)

Can anyone tell me the best / easiest way to do this in Exchange 2003? Thanks!

Answer : Lock Down TCP 25 on MS Exchange 2003

Hello JP,
  I think what they are asking you to do is to open your exchange system manager.  Expand Global Settings and go to the message delivery properties.  Click on connectoin filtering and click on accept and put in their ip addresses.  Then expand servers in system manager, expand your server, expand protocols, expand smtp, go to the properties of your virtual server, click advanced,click edit and make sure connection filtering is checked.  
  This is also going under the assumption that your exchange 2003 is running sp2.so that you have those options.