Enable sieve extension 'variables' on mail.archlinux.org

I'm subscribed to a few different Arch-related mailing lists and I'd like to be able to simplify my sieve config to this:

require ["regex", "fileinto", "mailbox", "variables"];

if header :regex ["From", "To", "CC"] "<(.*)@lists.archlinux.org>" {
  fileinto :create "${1}"; stop;
}

When I attempt to upload this to the server with sieve-connect, I receive the following error:

CHECKSCRIPT failed: NO {98}
line 4: error: require command: unknown Sieve capability `variables'.
error: validation failed.

If there is a better alternative, I'd love to know.

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