[Exim] acl_not_smtp

I've an MUA submitting mails on stdin.

It seems that acl_not_smtp has no access to "local_parts".
Given that a good To: header has been given by the time
the acl is run, why is this so? The headers must presumably
be parsed for recipients for delivery to happen at all,
surely?

Is the same likely to apply to "domains"?
What about $local_part and $domain?

LOG: MAIN REJECT
F=<helpdesk@???> rejected by non-SMTP ACL: cannot test
local_parts condition in non-SMTP ACL

Thanks,
     Jeremy