What to Do If Your Organization's IP Address is Blocked By Another Exchange 2007 Organization
Applies to: Exchange Server 2007 SP1, Exchange Server 2007
Topic Last Modified: 2007-05-30
This topic provides information about how to troubleshoot situations when the IP address of your organization's sending server is blocked by another Microsoft Exchange Server 2007 organization.
This problem can occur when the one or both of the following conditions are true:
The IP address of your Internet-facing sending server has been added to an IP Block List provider service. IP Block List provider services compile lists of IP addresses from which spam has originated in the past. Additionally, some IP Block List providers provide lists of IP addresses for which Simple Mail Transfer Protocol (SMTP) is configured for open relay. There are also IP Block List provider services that provide lists of IP addresses that support dial-up access.
Your IP address has been added to an organization's IP Block list because the organization has enabled sender reputation processing. Sender reputation is anti-spam functionality that is enabled on computers that have the Edge Transport server role installed to block messages according to many characteristics of the sender. Sender reputation relies on persisted data about the sender to determine what action, if any, to take on an inbound message. If your e-mail traffic patterns and content appear spam-like, sender reputation processing may frequently add your IP address to the organization's temporary IP Block list.
If you cannot send mail to another Exchange 2007 organization because your IP address is on an IP Block list, do one of the following:
Contact the IP Block List provider service and ask that your IP address be removed from their list.
Contact the receiving Exchange 2007 organization and request that the IP address of your sending server be added to that organization's IP Allow list. This action will ensure that anti-spam filters are bypassed for e-mail messages that originate from your servers. However, this action also requires the receiving administrator to trust that e-mail from your organization will not include spam, malware, or inappropriate content.
Make sure that your outbound SMTP commands are compliant, specifically with regard to the HELO/EHLO commands.
Verify that the SMTP server that you send from is not configured incorrectly as an open proxy.