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
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