How to Add SMTP Verb Commands to ISA Server 2006

Exchange 2007

Microsoft Exchange Server 2007 will reach end of support on April 11, 2017. To stay supported, you will need to upgrade. For more information, see Resources to help you upgrade your Office 2007 servers and clients.


Applies to: Exchange Server 2007, Exchange Server 2007 SP1

Topic Last Modified: 2015-03-08

This topic explains how to resolve the problem of inbound Internet e-mail messages that are stuck in queues on the Edge Transport server when the Edge Transport server tries to send mail through Microsoft Internet Security and Acceleration (ISA) Server 2006, with SMTP filtering or Secure SMTP (SMTPS) filtering enabled, to internal Hub Transport servers. For more information about what causes inbound Internet mail messages to be stuck on Edge Transport server queues, see Messages Queue on an Edge Transport Server with 500 5.1.1 Unrecognized Command Error.

The following procedure explains how to use Microsoft Management Console (MMC) in ISA Server 2006 to add specific Microsoft Exchange Server 2007 SMTP verb commands to the SMTP Add-in filter of ISA Server 2006. Because the verb commands are not recognized by ISA Server 2006, you have to add these commands. By running this procedure, you can clear the mail queues on the Edge Transport server and thereby enable inbound Internet mail to flow between Exchange transport servers in the perimeter network of your Exchange 2007 organization.

For more information about an alternative method to clear the mail queues on Edge Transport server, see How to Disable the SMTP Filter or SMTPS Filter on Firewall Policy Rule on ISA Server 2006.

To perform this procedure, the account you use must be delegated the following permissions:


ISA Server 2006 edition Permission

Standard Edition

ISA Server Full Administrator

Enterprise Edition

ISA Server Enterprise Administrator

Before you perform the following procedure, you should be aware of the following:

  • The additional Simple Mail Transfer Protocol (SMTP) commands should be enabled on only the Exchange transport rules that exist for Hub Transport server and Edge Transport server communication.

  • The SMTP filter on the firewall policy rule, which exposes an Edge Transport server to the Internet, should be set so that it does not advertise internal network specific extensions like X-AnonymousTLS and X-EXPs to the Internet. These SMTP verbs are only required by the internal Send connector on the Edge Transport server in order to authenticate to servers that are running Exchange (Exchange 2007 or earlier versions of Exchange Server) inside the Exchange organization and do not have to be advertised externally.

  • The SMTP verbs are as follows:


    • DSN




    • AUTH


    • 8BITMIME



    • XEXCH50

    • SIZE

  1. In the console tree of ISA Server Management, select the Configuration node, and then click Add-ins.

  2. On the details pane, right-click SMTP Filter, and then click Properties.

  3. On the SMTP Commands tab, click Add.

  4. In the SMTP Command Rule dialog box, make sure that Enable SMTP Command is checked.

  5. In Command Name, specify the name that you want to add.

  6. In Maximum Length, specify the maximum length in bytes.

  7. Click OK to close the dialog box.

  8. Click OK to close the SMTP Filter Properties page.

  9. In the details pane, click Apply to save the configuration changes.