mail server problem(postfix)

[Ankush Grover]

hey friends,

 My  Mail Server is configured on FC3
(Postfix+Dovecot+Clamav+Fetchmail).I am facing one problem few of the 
mails from my domain are getting rejected.

For example if any user from my domain is sending the mail to a user
on rediffmail.com domain that mail is getting rejected.

My Scenario is such we have one catchall with the ISP i download all
the mails from the ISP mailbox through fetchmali.For sending the mails
the local mail server with postfix running on it.The postfix  is
configured to authenticate with the ISP mail server before sending the
mails.

If the authentication is properly configured then why the mails are
getting rejected see below

ankush1711 at rediffmail.com>: host mail2.rediffmail.com[203.199.83.4] said: 553
    Message from xx.xx.xx.xx( Public Ipaddress of my company)  rejected - see
    http://spamblock.outblaze.com/xx.xx.xx.xx (in reply to RCPT TO command)


The link 
http://spamblock.outblaze.com/xx.xx.xx.xx (in reply to RCPT TO command ) 
shows this:


Explanatory Note : 


Your mail has been rejected because it has been sent direct from a mailserver
running on a dialup or other dynamic IP listed in the SORBS DUHL dynamic IP
blocklist at www.sorbs.net

We block mail from known dialup pools and other dynamic IP blocks, due to the
ever present risk of "direct to MX" spam originating from spammers running
bulkmailer software equipped with smtp engine capablities, and "remailer" virii
such as Swen and Sobig, which have their own smtp engines to remail copies of
themselves.

Please set your mailserver up so that it sends out mail through your ISP's
mailserver, or through any other mailserver with a static IP address that you
have access to. http://www.mail-abuse.com/support/an_rteoutgoing.html
is an excellent
resource which lists the steps required to set up a "smarthost" in several
mailservers.

This list is maintained by SORBS. If you believe this entry to be in error 
and you are actually a static IP, please submit a request using this form:
https://www.dnsbl.sorbs.net/scgi-bin/dulexclusions

Thanks,
Outblaze Postmaster (postmaster at outblaze.com)



How to stop my mail server to become a part of Spam World. I want to 
test that my local mail server is getting authenticated with the ISP
mail server.Sasl_finger is a tool that I know shows some statistics
regarding this but it does not itself checks by sending a mail.Is
there any other tool for checking the authentication with the ISP .

We have one Public IPaddress ,NAT is configured on the ADSL Router to
give all the users in the LAN access to the Internet.

In postfix/main.cf the entries for authentication as below:

smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/passwd
smtp_sasl_security_options = noanonymous

I have not configured TLS/SSL for postfix.

The entries for passwd file are as 

ISP mailserver            username:password.

Please guide me what wrong I am doing and how to correct it .

Thanks & Regards

Ankush