SOS!!! Promail problem!!!

I setup promail on Solaris2.5.

I tried the following lines in .forward, none of them worked:

"|IFS=' ';exec /usr/local/bin/procmail -f- #username"
"|IFS=' ';exec /usr/local/bin/procmail -f- USER=username"
"|exec /usr/local/bin/procmail #username"
"|exec /usr/local/bin/procmail USER=username"
and also switch the leading "| to |" for above cases.

I got this Return mail message for all the above cases:

Returned mail: Address <username(_at_)hostname(_dot_)(_dot_)(_dot_)> is unsafe 
for mailling to
programs

I have no idea what's this means.

Can anyone help??

I'll be very very very appreciated!!!

thanks so much,
Yvonne