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: 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:
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:
- If you want to implement a filter based on keywords, note that the "virus" keyword filters any incoming messages that have "virus" in any part of the message that is specified in the filter properties. For example, if the "virus" keyword is used, messages with "viruses," "antivirus," and other similar words are filtered. This limitation occurs even if you enclose the keywords in quotation marks.
- Wildcard characters (*) are not permitted.
- Click Start, click Programs, click Microsoft ISA Server, and then click ISA Management.
- Expand Servers and Arrays, expand Server_name, and then expand Extensions.
- Click Application Filters.
- In the right pane, right-click the SMTP filter, and then click Properties.
NOTE: By default, this filter is not turned on.
- Click the Attachments tab, and then click Add.
- Click Attachment Extension, and then type .test in the Attachment Extension box.
- Make sure that Delete message appears in the Action box.
- Click OK, and then click OK.
- Right-click SMTP Filter, and then click Enable.
- Click Save the changes and restart the service(s), and then click OK.
It may take several minutes for the SMTP filter to become active.
- Send a message that has an attachment that has a .test file name extension (for example, Textfile.test) from an external e-mail system (for example, Hotmail) to a user on the SBS 2000-based domain.
- After you send the message, check the mailbox of the user to whom you sent the message to confirm that the message does not appear in the user's mailbox.
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:
Article ID: 320703 - Last Review: Nov 11, 2008 - Revision: 1