Okay- couple of things:
1. Looks like the IP address you're using for your MX record is blacklisted by at least AT&T, and most likely others. That will certainly contribute to email problems. If the address you're using for your MX record is a statically assigned IP address, ask your ISP to add create a PTR record for you that matches your A record:
184.108.40.206.in-addr.arpa name = 24-180-57-228.dhcp.rvsd.ca.charter.com.
2. You need to check your /etc/postfix/main.cf- specifically, your 'myhostname', 'mydomain' and the 'mydestination' parameters:
"Sep 16 16:20:57 lianli postfix/smtp: 2624D47EE6D: to=<email@example.com>, orig_to=<firstname.lastname@example.org>, relay=mail.pressure-parts.com[220.127.116.11]:25, delay=0.76, delays=0.32/0.04/0.39/0, dsn=5.4.6, status=bounced (mail for mail.pressure-parts.com loops back to myself)"