[exim] conditions for running spam tests

I have the following in my acl_check_data:

  warn    spam       = nobody
          condition  = ${if < {$message_size}{10K}}
          add_header = X-Spam_score: $spam_score\n\
                       X-Spam_score_int: $spam_score_int\n\
                       X-Spam_bar: $spam_bar\n\
                       X-Spam_report: $spam_report

  # reject spam with high scores
  deny    message    = This message scored $spam_score points.
          spam       = nobody:true
          condition  = ${if < {$message_size}{10K}}
          condition  = ${if > {$spam_score_int}{70}{1}{0}}


This is working well enough, but I'd like to skip these tests under
certain conditions:

    * if the sender is on the localhost
    * if the message wasn't originally sent with SMTP
      (I have scripts on the server which send mail to me
      by calling Exim directly)
    * if the sender is authenticated

I'm a little fried after a solid week of trying to rebuild this
system, and I can't seem to figure these out.

If the answers are in the FAQ and I missed them, I'm sorry. I did look.

Any suggestions?