xclient

Enables or disables the passing of the XCLIENT command with client parameters when connecting to the SMTP backend.

With XCLIENT, the MTA is able to write client information to the log and apply various limitations based on this data.

If XCLIENT is enabled then nginx passes the following commands when connecting to the backend:

• EHLO with the server name
• XCLIENT
• EHLO or HELO, as passed by the client

If the name found by the client IP address points to the same address, it is passed in the NAME parameter of the XCLIENT command. If the name could not be found, points to a different address, or resolver is not specified, the [UNAVAILABLE] is passed in the NAME parameter. If an error has occurred in the process of resolving, the [TEMPUNAVAIL] value is used.

If XCLIENT is disabled then nginx passes the EHLO command with the server name when connecting to the backend if the client has passed EHLO, or HELO with the server name, otherwise.