DOCUMENT:Q194742  13-MAY-2000  [exchange]
TITLE   :XFOR: Internet Mail Service Support for user@[IP Address] Format
PRODUCT :Microsoft Exchange
PROD/VER:winnt:5.5
OPER/SYS:
KEYWORDS:exc55

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Exchange Server, version 5.5 
-------------------------------------------------------------------------------


SUMMARY
=======

In Exchange Server versions 4.0 and 5.0, it is not possible to send messages to
a user by using the following format:

   user@[IP Address]

However, in accordance with for Request for Comments (RFC) 821 and 821bis, this
is a valid addressing format.

Microsoft recognizes the need for compliance to this RFC specification. Microsoft
Exchange Server version 5.5 allows for this addressing method and therefore
allows messages to be sent by using this format. The feature involves a
modification to the Exchange Server Internet Mail Service to understand IPv4
literals. The Internet Mail Service is now capable of accepting mail inbound,
delivering outbound, and rerouting mail addressed in the format "user@[IP
Address]," also known as IPv4 literal.

NOTE: The admin does not allow you to create a proxy of the form 'user@[IP
Address]' (it strips the brackets).

For additional information, click the article number below to view the article in
the Microsoft Knowledge Base:

   Q193316 XFOR: How to create addresses of form 'user@[IP Address]


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

Per RFC 821 page 31:

   Hosts are generally known by names, which are translated to addresses in each
   host. Note that the name elements of domains are the official names -- no use
   of nicknames or aliases is allowed. Sometimes, a host is not known to the
   translation function and communication is blocked. To bypass this barrier,
   two numeric forms are also allowed for host "names". One form is a decimal
   integer prefixed by a pound sign, "#", which indicates the number is the
   address of the host. Another form is four small decimal integers separated by
   dots and enclosed by brackets, for example, "[123.255.37.2]", which indicates
   a 32-bit ARPA Internet Address in four 8-bit fields.

NOTE: The other message format that is noted in this section of RFC 821 is the
following

   user@#xxxxxxxxx

where xxxxxxxx is a decimal number that corresponds to the host address of the
computer. The Internet Mail Service on all versions of Exchange Server including
Exchange 2000 Server does not support this type of addressing.



Additional query words: IPv4-literal, RFC821, 821bis

======================================================================
Keywords          : exc55 
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : winnt:5.5
Issue type        : kbinfo

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2000.