DISABLE_ADDRESS

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TCP/IP-channel-specific options: DISABLE_ADDRESS (0 or 1)

The MTA's SMTP server implements a private command XADR. This command returns information about how an address is routed internally by the MTA as well as general channel information. Releasing such information may consistute a breach of security for some sites. Settting the SMTP server option DISABLE_ADDRESS to 1 disables the XADR command, so that the SMTP server returns the response


550 5.7.0 XADR command has been disabled. 

to XADR attempts. The default is 0, which enables the XADR command. In 8.0, the default has changed to 1, disabling the XADR command.

SMTP server probes of the PORT_ACCESS mapping table can enable use of XADR (overriding a more general DISABLE_ADDRESS=0 setting) for connections from particular source IPs (e.g., the host itself, 127.0.0.1, and particular administrator systems) via the (new in 7.0) $V flag.


See also: