xclient

The xclient directive is utilized within the NGINX Mail Core to manage the inclusion of the remote client's IP address in the X-Client header of outgoing mail server responses. This can be particularly useful in scenarios where tracing or logging the actual client's IP address is necessary, especially when requests are proxied through another server or when implementing security measures that rely on knowing the original source of a request.

When enabled, the NGINX application inserts the client's IP into the X-Client field of the mail protocol headers, which can then be utilized by the backend mail handler or logging service. This directive accepts a flag argument that allows administrators to toggle this behavior on or off. It's important to configure this directive properly to avoid potential privacy issues, as revealing client IP addresses may not be appropriate in all contexts.

The supported contexts for this directive are within the mail block and the mail server configurations. This allows for flexible configuration depending on the specific server instance deployments, assisting in maintaining logs that reflect authentic client connections, enhancing traceability for various audit purposes.