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

The MTA's SMTP server implements a private command XCIR. This command returns MTA circuit check information. Releasing such information may consistute a breach of security for some sites. Setting the SMTP server option DISABLE_CIRCUIT to 1 disables the XCIR command, so that the SMTP server responds with the error

550 5.7.0 XCIR command has been disabled. 

to any XCIR command attempts. Setting DISABLE_CIRCUIT to 0 enables the XCIR command. If DISABLE_CIRCUIT is not explicitly set, then use of the XCIR command is controlled by the DISABLE_GENERAL TCP/IP-channel-specific option setting. In 8.0, the default has changed to 1, disabling the XCIR command.

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

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