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Possible SMTP proxy detected

[This topic is intended to address a specific issue called out by the Exchange Server Analyzer Tool. You should apply it only to systems that have had the Exchange Server Analyzer Tool run against them and are experiencing that specific issue. The Exchange Server Analyzer Tool, available as a free download, remotely collects configuration data from each server in the topology and automatically analyzes the data. The resulting report details important configuration issues, potential problems, and nondefault product settings. By following these recommendations, you can achieve better performance, scalability, reliability, and uptime. For more information about the tool or to download the latest versions, see "Microsoft Exchange Analyzers" at https://go.microsoft.com/fwlink/?linkid=34707.]  

Topic Last Modified: 2006-12-06

The Microsoft® Exchange Server Analyzer Tool tries to send a message to the Postmaster account or a user-defined account for the Simple Mail Transfer Protocol (SMTP) domain.

The following default response is expected when the Exchange Server Analyzer opens a socket connection to the SMTP server:

"220 Computer Name . Domain Name .com Microsoft ESMTP MAIL Service, Version: Version Number ready at Date Time +0000"

If the Exchange Server Analyzer receives a non default response that contains a third-party-specific string, the Exchange Server Analyzer displays an error.

This error indicates that there may be a third-party SMTP proxy server that is running behind the remote server.

If the default SMTP banner has not been intentionally customized by the Exchange Server administrator, this warning may indicate that the Exchange Server is behind an SMTP proxy that is filtering the Exchange Server Extended Simple Mail Transfer Protocol (ESMTP) commands.

If Exchange Server ESMTP commands are filtered, this can have a significant effect on Exchange performance and may produce the behavior described in Microsoft Knowledge Base article 320027, "Cannot send or receive e-mail messages behind a Cisco PIX firewall" (https://go.microsoft.com/fwlink/?linkid=3052&kbid=320027).

For more information about customized SMTP banners, see the following Microsoft Knowledge Base article: