How to stop Exchange Server Relay
If you’re a Microsoft Exchange server Admin part of your job is to keep your organization free of SPAM.
Regardless of how much bandwidth your organization may have, there is a finite amount of data that the Internet connection can handle in a given amount of time. This means that if your organization is using their Internet connection at or near its total capacity then any time you receive a junk E-mail message, other legitimate messages are kept waiting until bandwidth becomes available. Additionally, organizations plagued by excessive SPAM, reduces available disk space on an Exchange Server. So as you can see it’s imperative that you effectively combat SAPM.
The Microsoft Exchange Server Internet Mail Service may be configured as a publicly accessible relay mail. In this configuration, the outside users can use the relay Internet Mail Service as an agent for unsolicited commercial e-mail (UCE or SPAM), flooding others with many copies of the same message.
To prevent this from happing, first, make sure that the default SMTP relay settings have been applied to your Exchange 2003 servers per Microsoft’s article on how to configure SMTP relay restrictions. If your Exchange server is still sending SPAM, then you should disable all authentication methods except for “anonymous” on your Internet-facing SMTP host. By default, anonymous authentication, will allow messages to be sent, but not relayed.
If outbound SPAM remains a problem, then the SPAM is coming from one of your internal hosts. You may consider resetting all passwords in your Exchange organization to regain control over the SMTP relaying, or reset the Relay Restrictions tab to “Allow all computers which successfully authenticate to relay, regardless of the list above.”
For more information, read Microsoft’s article, Stop Exchange Server SPAM from the inside by locking down SMTP.
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