use_splice

Since: Version 2026.03.04-bb93ecb1

The functionality described in this section requires version 2026.03.04-bb93ecb1 of KumoMTA, or a more recent version.

On Linux, the proxy server uses splice(2) for efficient zero-copy data transfer between the client and remote connections. This can significantly reduce CPU usage for high-throughput proxy scenarios.

Set this to false to disable splice and use regular userspace copying instead. This may be useful for debugging or if you encounter issues with splice on your system.

The default is true (splice is enabled on Linux).

Note: splice(2) is only used for plain TCP connections. TLS connections always use regular copying because the data must be decrypted/encrypted in userspace.

proxy.start_proxy_listener {
  listen = '0.0.0.0:1080',
  use_splice = false,
}