XFOR: Internet Mail Service Support for user@[IP Address] Format in Accordance with RFC 821 (194742)

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:

193316 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.