Sending mails using postfix to gmail account
 

I have a problem with using postfix for sending mails to my gmail account.
Here is the error that I get in /var/log/mail.log
Feb 3 17:15:01 RISH postfix/pickup[14115]: 703D9162871: uid=33 from=<www-data>
Feb 3 17:15:01 RISH postfix/cleanup[14133]: 703D9162871: message-id=<20130203114501.703D9162871@noreply.purposenet. com>
Feb 3 17:15:01 RISH postfix/qmgr[14116]: 703D9162871: from=<www-data@purposenet.com>, size=3183, nrcpt=1 (queue active)
Feb 3 17:15:01 RISH postfix/error[14122]: 703D9162871: to=<chandni.247@gmail.com>, relay=none, delay=0.14, delays=0.09/0/0/0.05, dsn=4.3.0, status=deferred (unknown mail transport error)

hostname
RISH

hostname -f
RISH

cat /etc/hosts
127.0.0.1 localhost
127.0.1.1 RISH
10.2.8.87 master
10.3.10.154 slave
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

I need to send a mail from the localhost to my gmail account. Could someone please help me with this..

Does this happen only for Gmail addresses?

What's in /etc/postfix/main.cf and /etc/postfix/master.cf?