DSN support and relaying problem

Hi 

I'd like to ask you about dsn support.
My server works like gateway, relays mails to destination server.
When i tried to send an email with dsn features: 
.....
rcpt to:rcpt_address <at> domain.com notify=success,failure,delay
.....
i get the delivery answer from gateway and not from destination server.
And I'd say that this is wrong, cause gateway should just relay message.
( rfc - http://www.cse.ohio-state.edu/cgi-bin/rfc/rfc1891.html), cause
gateway cannot say if it was delivered succesfull, it does destination
server.

Logs: 
May 14 15:23:11 mail postfix/qmgr[4008]: E026CA21F3:
from=<sender_address <at> one.domain.com>, size=973, nrcpt=1 (queue active)
May 14 15:23:11 mail postfix/smtpd[4086]: disconnect from
localhost[127.0.0.1]
May 14 15:23:11 mail amavis[2477]: (02477-01) Passed CLEAN,
[212.67.79.185] [212.67.79.185] < sender_address <at> one.domain.com > -> <
rcpt_address <at> domain.com >, Message-ID:
<20080514132259.5135BA21C5 <at> mail.domain.com >, Hits: 4.184, 5456 ms
May 14 15:23:11 mail postfix/smtp[4079]: 5135BA21C5: to=<
rcpt_address <at> domain.com >, relay=127.0.0.1[127.0.0.1]:10024, delay=38,
delays=32/0.01/0.01/5.5, dsn=2.6.0, status=sent (250 2.6.0 Ok,
id=02477-01, from MTA: 250 2.0.0 Ok: queued as E026CA21F3)
May 14 15:23:11 mail postfix/cleanup[4078]: 1D095A21F4:
message-id=<20080514132311.1D095A21F4 <at> mail.domain.com >
May 14 15:23:11 mail postfix/smtp[4088]: E026CA21F3: to=<
rcpt_address <at> domain.com >, relay=xxxxxxx[xxxxxxx]:25, delay=0.25,
delays=0.1/0.06/0/0.09, dsn=2.6.0, status=sent (250 2.6.0
<20080514132259.5135BA21C5 <at> mail.domain.com > Queued mail for delivery)
May 14 15:23:11 mail postfix/bounce[4089]: 5135BA21C5: sender delivery
status notification: 1D095A21F4
May 14 15:23:11 mail postfix/qmgr[4008]: 5135BA21C5: removed
May 14 15:23:11 mail postfix/qmgr[4008]: E026CA21F3: removed
May 14 15:23:11 mail postfix/qmgr[4008]: 1D095A21F4: from=<>, size=2334,
nrcpt=1 (queue active)
May 14 15:23:11 mail postfix/smtp[4088]: 1D095A21F4: to=<
sender_address <at> one.domain.com >, relay=sender.server[xxxxxxx]:25,
delay=0.67, delays=0.07/0/0.27/0.33, dsn=2.0.0, status=sent (250 Ok:
queued as 5A5A713C0D2)

How can i change it ? probably there is some parameter

Thx

pet