REVERSE DNS HELP

[Kris McElroy]

I inherited a Linux DNS server.  I received a call today from a user and they said their emails were being rejected by a certain host.  I checked into the problem and found that it was a reverse DNS issue on our part.  My question is I have to styles of reverse dns files listed below:  which one is correct if either and what is the correct (proper) format for a reverse DNS file?  What is the difference between the @ and the IN?  I am very new to DNS!  


1st style:

@                       NS       Ns1.duracom.net
@                       NS       ns2.duracom.net
$Generate  0-255  $         PTR        $.sb10.duracom.net


2nd style:


IN                        NS    ns1.duracom.net    
IN                        NS    ns2.duracom.net
21                        mail.whatever.com
22                        www.whatever.com



Thanks,


Kris McElroy
kmcelroy at duracom.net

Internet Systems Engineer
Duracom, INC.