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

RFC 821 and 821bis compliance requires the support of IPv4 literals (user@[IP address]).

The Exchange Server version 5.5 Internet Mail Service now supports addresses containing IPv4 literals (user@[IP address]) inbound, outbound, and rerouted. A message is routed inbound if the IPv4 literal is one of the Exchange Server computer's IP addresses.

A message that is routed inbound is only delivered if it matches a proxy. However, the Administrator program strips the square brackets from the address when you try to create an address of the form "user@[IP address]" from the user interface.

To create a proxy of the type "user@[IP address]", perform the following steps:

WARNING: Using the raw mode of the Exchange Server Administrator program (admin /r) incorrectly can cause serious problems that may require you to reinstall Microsoft Windows NT Server and/or Microsoft Exchange Server. Microsoft cannot guarantee that problems resulting from the incorrect use of raw mode can be solved. Use raw mode at your own risk.

1. Start the Microsoft Exchange Administrator program in raw mode by typing the following text at a command prompt:
   admin /r
   Note You may have to include the full path (Exchsrvr\Bin\Admin /r).
2. After the Administrator program is running in raw mode, open the Recipient container where the user who needs the special proxy address is located.
3. With the user highlighted, click File, and then select Raw Properties from the menu bar, or press SHIFT+ENTER.
4. In the property window that appears for the user object, click E-mail Addresses under the Object attributes.
5. Under the attribute values section, edit the value field that contains the new e-mail address--for example, type SMTP:user@[1.2.3.4].
   
   Click the ADD button to add to the list of available e-mail addresses. Close the raw properties of the mailbox.
6. Open the properties of the mailbox, and then click the E-mail address tab.
   
   Highlight the new e-mail address, and then click Edit. If the E-mail type field is empty, type SMTP. Click OK to close the properties window.
7. Note The following step may not be needed in all configurations.
   
   Open the properties of the IMS and select the routing tab. Add a domain of [IP Address] as inbound (Ex: [1.2.3.4]). This will allow the IMS to accept mail for this IP address if the Exchange Server's IP address does not match the IP address of the SMTP address.

Per RFC 821 page 31:

Hosts are generally known by names that 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, e.g., "[123.255.37.2]", which indicates a 32-bit ARPA Internet Address in four 8-bit fields.