Article ID: 320027 - View products that this article applies to.
This article was previously published under Q320027
Important This article contains information that shows you how to help lower security settings or how to turn off security features on a computer. You can make these changes to work around a specific problem. Before you make these changes, we recommend that you evaluate the risks that are associated with implementing this workaround in your particular environment. If you implement this workaround, take any appropriate additional steps to help protect the computer.
You may experience one or more of the following behaviors:
This issue may occur in the following situation:
220*******************************************************0*2******0***********************For more information, visit the following Cisco Web sites:
Old versions of PIX or ASA:
220 SMTP/cmap_________________________________________ read
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_tech_note09186a00800b2ecb.shtmlNote If you have an ESMTP server behind the PIX or ASA firewall, you may have to turn off the Mailguard feature to permit mail to flow correctly. Also, establishing a Telnet session to port 25 may not work with the fixup protocol smtp command, especially with a Telnet client that uses character mode.
Note Besides the Cisco PIX or Cisco ASA firewall, there are several firewall products that have SMTP Proxy capabilities that may produce the issues that are mentioned earlier in this article. The following is a list of firewall manufacturers whose products have SMTP Proxy features:
For additional information, visit the Web sites listed in the "More Information" section.
Warning This workaround may make a computer or a network more vulnerable to attack by malicious users or by malicious software such as viruses. We do not recommend this workaround but are providing this information so that you can implement this workaround at your own discretion. Use this workaround at your own risk.
Note A firewall is designed to help protect your computer from attack by malicious users or by malicious software such as viruses that use unsolicited incoming network traffic to attack your computer. Before you disable your firewall, you must disconnect your computer from all networks, including the Internet.
To resolve this issue, turn off the Mailguard feature of the PIX or ASA firewall.
Warning If you have an ESMTP server behind the PIX or ASA, you may have to turn off the Mailguard feature to make it possible for mail to correctly flow. If you use the Telnet command to port 25, this may not work with the fixup protocol smtp command, and this is more noticeable with a Telnet client that performs character mode.
To turn off the Mailguard feature of the PIX or ASA firewall:
The PIX or ASA Software Mailguard feature (also called Mailhost in early versions) filters Simple Mail Transfer Protocol (SMTP) traffic. For PIX or ASA Software versions 4.0 and 4.1, the mailhost command is used to configure Mailguard. In PIX or ASA Software version 4.2 and later, the fixup protocol smtp 25 command is used.
Note You must also have static IP address assignments and conduit statements for your mail server.
When Mailguard is configured, Mailguard allows only the seven SMTP minimum-required commands as described in request for comment (RFC) 821, section 4.5.1. These seven required commands are the following:
HELOOther commands, such as KILL and WIZ are not forwarded to the mail server by the PIX or ASA firewall. Early versions of the PIX or ASA firewall return an "OK" response, even to commands that are blocked. This is intended to prevent an attacker from the knowledge that the commands have been blocked.
To view RFC 821, visit the following RFC Web site:
http://www.faqs.org/rfcs/rfc821.htmlAll other commands are rejected with the "500 Command unrecognized" response.
On Cisco PIX and ASA firewalls with firmware versions 5.1 and later, the fixup protocol smtp command changes the characters in the SMTP banner to asterisks except for the "2", "0", "0 " characters. Carriage return (CR) and linefeed (LF) characters are ignored. In version 4.4, all characters in the SMTP banner are converted to asterisks.
Test Mailguard for proper functionBecause the Mailguard feature may return an "OK" response to all commands, it may be hard to determine whether it is active. To determine whether the Mailguard feature is blocking commands that are not valid, follow these steps.
Note The following steps are based on PIX or ASA software version 4.0 and 4.1. To test later versions of PIX or ASA software (version 4.2 and later), use the fixup protocol smtp 25 command and the appropriate static and conduit statements for your mail server.
With Mailguard turned off
With Mailguard turned on
By default, the PIX or ASA firewall blocks all outside connections from accessing inside hosts. Use the static, access-list, and access-group command statements to permit outside access. For additional information about these commands, visit the following Cisco Web site:
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_60/config/commands.htmFor additional information about how to configure the Cisco PIX or ASA firewall, please visit the following Cisco Web sites:
For more information about firewall products that have SMTP Proxy capabilities, visit the following Web sites:
http://www.symantec.com/business/index.jspThe third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.
Article ID: 320027 - Last Review: January 18, 2011 - Revision: 15.0
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