Sendmail with Multi Domains on my server

hi all,

I have 1 machine with Dynamic IP and linux server(LAMP), postfix for mail, I am hosting 3 websites each website has a php application page where I ask people information and submit to me by email and also the visitor receive a email confirmation, so the php app send 2 emails. My server not receive emails, all 3 email contact are hosted by 3th companies(zoneedit,godaddy), forwaring the info to my gmail account,so, my server just send email.

Now, the php app is working fine just for the first domain, and the issue is that I am not receiving email from the others 2 domain

In the beginning, when I setup the server I never setup postfix, so I think is setup just for one domain, and when the php app send the email it don't go through the ISP.
I really do not know how to setup the postfix to send email on the same machine as info@my1domain.com, info@my2domain.com info@my3domain.com.

this is my postconf -n

alias_maps = hash:/etc/postfix/aliases, hash:/var/lib/mailman/data/aliases
command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/lib/postfix
delay_warning_time = 4h
html_directory = /usr/share/doc/postfix-2.1.4/html
inet_interfaces = localhost
mail_owner = postfix
mailq_path = /usr/bin/mailq.postfix
manpage_directory = /usr/share/man
mynetworks_style = host
newaliases_path = /usr/bin/newaliases.postfix
owner_request_special = no
queue_directory = /var/spool/postfix
readme_directory = /usr/share/doc/postfix-2.1.4/README_FILES
recipient_delimiter = +
sample_directory = /usr/share/doc/postfix-2.1.4/samples
sendmail_path = /usr/sbin/sendmail.postfix
setgid_group = postdrop
smtpd_banner = $myhostname ESMTP $mail_name ($mail_version) (Mandrake Linux)
smtpd_sasl_path = /etc/postfix/sasl:/usr/lib/sasl2
unknown_local_recipient_reject_code = 450


somebody can help me, I will really appreciate

PD: I read all about postfix.org but I need some other help to decided what I need to do.

i sincerely hope you have managed to fix this by now else you have probably killed yourself out of sheer frustration but just in case, have you checked the logs to see if the emails are actually being sent else, have you created suitable MX records ?