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Q305007: XCON: You Cannot Send SMTP Mail Through a Firewall

Article: Q305007
Product(s): Microsoft Exchange
Version(s): 5.5
Operating System(s): 
Keyword(s): 
Last Modified: 27-MAR-2002

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The information in this article applies to:

- Microsoft Exchange Server, version 5.5 
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SYMPTOMS
========

If you send a message to a Simple Mail Transfer Protocol (SMTP) recipient over
the Internet Mail Service by using Microsoft Outlook Express or any other Post
Office Protocol version 3 (POP3) or Internet Message Access Protocol Version
4rev1 (IMAP4) client, you may receive a non-delivery report (NDR) that is
similar to:

  The message could not be sent because one of the recipients was rejected by
  the server. The rejected e-mail address was 'XXX@XXX.XXX'. Subject 'XXXX',
  Account: 'XXX', Server: 'XXX.XXX.XXX.XXX', Protocol: SMTP, Server Response:
  '550 Requested action not taken: mailbox unavailable', Port: 25, Secure(SSL):
  No, Server Error: 550, Error Number: 0x800CCC79

CAUSE
=====

This issue may occur if:

- Rerouting is selected on the Routing tab of the Internet Mail Service.

-and-

- The "Hosts and clients that successfully authenticate" routing restriction is
  selected.

-and-

- A Watchguard Firebox firewall is being used.

The Watchguard Firebox firewall can be configured to strip SMTP commands. To use
authentication, the following command verbs must be turned on:

- Auth

- Auth-logon

If the authentication headers are denied on the firewall, the mail flow is
stopped externally.

RESOLUTION
==========

To resolve this issue, configure the firewall to allow all of the Exchange
Server SMTP command verbs to pass through. If you have to, turn off the headers
that are being stripped one by one.

MORE INFORMATION
================

Determine whether or not you can successfully send mail from a POP3 or IMAP4
client if you connect directly to the Exchange Server computer, instead of
connecting through the firewall.

Additional query words: IMS

======================================================================
Keywords          :  
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : :5.5
Issue type        : kbprb

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