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HOW TO: Configure the SMTP Filter in ISA Server to Block SMTP E-mail Attachments by File Name Extension in SBS
Article ID: 320703 - View products that this article applies to.
This article was previously published under Q320703
This step-by-step article describes how to configure the default Microsoft Internet Security and Acceleration (ISA) Server Simple Mail Transfer Protocol (SMTP) application filter on Small Business Server (SBS) 2000 to delete incoming e-mail messages that contain an attachment that has a specific file name extension.
There are other settings for the SMTP application filter in ISA Server. This article is intended to provide a simple example of the functionality of the SMTP application filter.
By default, you cannot implement the SMTP Commands section of the SMTP filter in SBS 2000. For information about how to use the SMTP Commands functionality of the SMTP filter, visit the following Microsoft Web site:
Configuring and Securing Microsoft Exchange 2000 Server and Clients white paperNote that the white paper on this Web site suggests advanced modifications to ISA Server. These advanced modifications are outside the scope of this article and are typically not used in an SBS 2000 environment. If you follow the procedure that is described in this white paper to implement the SMTP Commands functionality, the auth command is not defined. As a result, external SMTP client computers cannot authenticate against the SBS 2000-based computer to send or receive e-mail messages.
NOTE: On an SBS 2000 installation that is using Microsoft Connector for POP3 Mailboxes, the SMTP filter also applies to messages that are delivered by using the POP3 Connector.
ISA Server Service Pack 1 (SP1) addresses several issues that pertain to the default SMTP filter. Microsoft recommends that you obtain and download ISA Server SP1 before you perform the procedure that is described in this article. To obtain ISA Server SP1, visit the following Microsoft Web site:
ISA Server Service Pack 1To confirm that ISA Server SP 1 is installed, start the Add/Remove Programs tool in Control Panel and confirm that "Microsoft ISA Server Service Pack 1 and Hot Fixes" is listed.
By default, the components that you must use to have full functionality of the SMTP filter are not installed on a stand-alone version of ISA Server (the non-SBS 2000 version). The integrated Setup program of ISA Server that is part of the SBS 2000 product suite does install the required components.
For additional information about ISA Server as a stand-alone product (the non-SBS 2000 version), click the article number below to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/315132/EN-US/ )HOW TO: Configure SMTP Message Screener in ISA Server 2000
A common implementation of this filter may cause e-mail messages that have attachments with .exe, .vbs, .bat file name extensions to be filtered and the action is "Delete."
If you implement ISA Server's SMTP filter, you may create additional overhead for the Inetinfo.exe process because the SMTP service runs under the context of Inetinfo.exe. If the SMTP filter is subjected to heavy loads, you may want to use the hotfix that is described in the following Microsoft Knowledge Base article:
(http://support.microsoft.com/kb/292010/EN-US/ )High Memory Consumption by SMTP Message Screener Under Stress
For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/305012/EN-US/ )How to Remove Corrupt Entries from the SMTP Filter
(http://support.microsoft.com/kb/312552/EN-US/ )How to Use the SPCheck Tool to Verify ISA Server Files
(http://support.microsoft.com/kb/292014/EN-US/ )Deleting Disabled SMTP Filter Attachment Rules Leaves Rule
(http://support.microsoft.com/kb/313344/EN-US/ )SMTP Filter Is Unstable When Using Space in Keyword, Attachment
(http://support.microsoft.com/kb/313345/EN-US/ )SMTP Filter UI Displays Red X Instead of Rules
(http://support.microsoft.com/kb/313396/EN-US/ )Attachment Rules for SMTP Filter May Become Damaged
(http://support.microsoft.com/kb/285812/EN-US/ )Cannot Configure or Use the SMTP Filter