Microsoft Exchange 2007 can be locked down to only accept email from the MailRoute servers by following these steps:
- Open Exchange Management Console
- Under the Server Configuration node, select Hub Transport
- Choose the receive connector you are using for your incoming SMTP traffic, right click and select Properties
- Click the Network tab
- Find where it says Receive mail from remote servers which have these IP addresses
- Select Add -> IP Address
In the Add IP address(es) of Remote Servers box, enter the MailRoute network in CIDR notation:
There is probably a default entry in there for an address range that will need to be removed, because it allows connection from any IP address. It looks like this:
0.0.0.0 - 255.255.255.255
These changes should take effect right away without having to restart any services, but we have seen some instances where a restart of Exchange services is required.
Microsoft has online documentation on how to do this at http://technet.microsoft.com/en-us/library/bb691331(EXCHG.80).aspx
You may need to refer to other sections of that technical reference document if your Exchange configuration is non-standard.
NOTE: If you stop receiving email and your configuration / firewall has not changed please check the permissions and select allow anonymous users
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
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