i recieved this today from a zimbra account

<ahoang@houwire.com>: host hwchp.houwire.com[] said: 421 hwchp has
refused your connection because your server did not have a PTR record. (in
reply to MAIL FROM command)

can someone tell me how to setup a PTR record and do i need to understand what a PTR record is in order to use Zimbra.

Thanks in advance.


Fedora Core4 Zimbra 3.0