RBL backscatterer.org mailnull and postmaster

[xabungo]

hI,

I start to receive a message that My server is listed in backscatterer.org.
I check there, and they say :
"You will either find that your system tried to send misdirected bounces or misdirected autoresponders to claimed but in reality faked senders, or your system tried sender verify callouts against our members near that time.

So you should look for outgoing emails that have a NULL SENDER or POSTMASTER in MAIL FROM."

I try to find in the SOLUTION IN HWM AND EXIM CONIF, but don't know where to start.

Can anyone help me with it?
I don't know how to!

Best Regards,

Ricardo Dias

[xabungo]

I start to beleive this is caused by a forum (agora forum) that I install few days ago.
Too many registers with mail from .pl