Postfix Problem

Helo
I have postfix serwer.
When my users send email localy is Ok.
When my users send email out of local network postfix reject it.
When i write there IP numbers to mynetworks all is OK
What can i do, I will relay access for tpnet.pl.
Where I may write it.
Oct 19 14:06:20 localhost postfix/smtpd[7230]: 95A1D684332: reject: RCPT
from bei146.neoplus.adsl.tpnet.pl[83.28.20.146]: 554 <gregmad@o2.pl>:
Relay access denied; from=<rcsa@uw.rzeszow.pl> to=<gregmad@o2.pl>
proto=SMTP helo=<rcsa>
Oct 19 14:49:47 localhost postfix/smtpd[8483]: 0ECF1684343: reject: RCPT
from pa241.chlopice.sdi.tpnet.pl[217.96.216.241]: 554
<kryla@sbcglobal.net>: Relay access denied;
from=<gchlopi@rzeszow.uw.gov.pl> to=<kryla@sbcglobal.net> proto=SMTP
helo=<pomost1>
Oct 19 14:49:57 localhost postfix/smtpd[8028]: 59334684343: reject: RCPT
from pa241.chlopice.sdi.tpnet.pl[217.96.216.241]: 554 <kryla@sbcglobal.net>:
Relay access denied; from=<gchlopi@rzeszow.uw.gov.pl> to=<kryla@sbcglobal.net>
proto=SMTP helo=<pomost1>

Please help.

Regards
Artur Slowik