How can I hide procmail's output from sendmail?

I bounce some (very specific, definitely spam) email with procmail 'exitcode=77'

Problem is that sendmail bounces the message back with the contents of my  
.forward (so the sender knows that it was delivered and then bounced).

How can I hide this from sendmail so the bounced-recipient gets no message  
but 'Permission denied' or some such?

Thanks again folks.

TjL


ps -- Hebrew started as of 2 July, and ends on 22 August, so
please understand if responses are slow.  I am taking a 2
semester class in 8 weeks for 6 credits

--
TjL <luomat peak org>
f ` cn rd ths ` my hv lrnd hbrw