The E-mail Firewall Service subscribes to the Spamhaus Block List (SBL) filter system of spam-blocking. The SBL is a continuously monitored database of IP addresses that determines whether or not e-mail is being sent by a verified spam source. For more information, see: http://www.spamhaus.org

Can I check myself to see if the sender is on the SBL list?
Do you have an e-mail message that you received previously from this person, organization, or e-mail list? You can check yourself to see if the IP address of the mail sender has been blocked.

• Configure your e-mail application to View full headers
• Identify the X-Originating-IP address
• Cut and paste that number into the Spamhaus Blocked Lookup field. If the results show, for example -- "Open Proxy: Spam Injection Site" -- this means that the sender is using an electronic post office that has been blocked

How will the sender be notified?
Senders of known spam that are blocked by the spam-blocking system will see bounced messages, for example:

550 5.7.1 Email rejected because 127.0.0.2 is listed by sbl-xbl.spamhaus.org
554 5.0.0 Service unavailable

The message means that the IP Address "127.0.0.2" is listed within their database of blocked addresses.