Microsoft Exchange 2003 and 2007 can be locked down to only accept email from the MailRoute servers by following these steps:
- Open Exchange System Manager
- Go to Servers -> [MailServer Name] -> SMTP
- Right click and go to Properties for Default SMTP Virtual Server
- Click the Access tab
- Click Connections
- Choose Only the List Below
- Click Add -> Group of Computers and enter our network block:
- Subnet Address: 188.8.131.52
- Subnet Mask: 255.255.248.0
Microsoft has an Administration Guide for Microsoft Exchange Server 2003 available at http://www.microsoft.com/downloads/en/confirmation.aspx?FamilyID=98e45481-1458-4809-97d6-50d8aeebd8a1&displaylang=en
NOTE: If you stop receiving email and your configuration / firewall has not changed, please check the permissions then select allow anonymous users.
Link to Microsoft Exchange Article About Permissions and Anonymous Users; http://technet.microsoft.com/en-us/library/bb629484(v=exchg.80).aspx
NOTE: Content Filters and Sender IDs need to be disabled on the Exchange server. If the server's mail traffic is filtered by MailRoute, it is not necessary to keep them enabled.
Please see our article on how to do this here